the behaviour of arsenic during jarosite precipitation- arsenic precipitation at 97°c from sulphate...
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Canadian Metallurgical Quarterly, Vol. 26, No.2, pp.91-101, 1987Printed in Great Britain.
0008-4433/87 $3.00+ .00© 1987 Canadian Institute of Mining and Metallurgy
Pergamon Journals Ltd.
THE BEHAVIOUR OF ARSENIC DURING JAROSITEPRECIPITATION: ARSENIC PRECIPITATION AT 97°C FROM
SULPHATE OR CHLORIDE MEDIA
J. E. DUTRIZAC and J. L. JAMBORMineral Sciences Laboratories, CANMET, Energy, Mines and Resources Canada, 555 Booth Street,
Ottawa, Ontario KIA OGl, Canada
(Received 5 November 1986)
Abstract- The behaviour of arsenic during the precipitation of alkali jarosite compounds at 97°C hasbeen investigated as a function of the arsenic and alkali concentrations, solution pH and dissolved ironconcentration. Arsenite is not precipitated, but arsenate phases are extensively eliminated with the jarositesformed from either sulphate or chloride media. Up to 90% of the initial arsenate can be precipitated,mostly as a separate phase but also as a limited solid solution in the jarosite. Although well crystallizedscorodite is formed in chloride media, an amorphous phase, chemically similar to scorodite, usuallyprecipitates in sulphate media at this temperature. The results obtained at 97°C suggest a limited solidsolubility of As04 ('" 2%) in the alkali jarosites, but this point requires confirmation.
INTRODUCTION
The precipitation of jarosite-type compounds (M Fe3(S04h(OH)6 where M = Na, K, Rb, NH4, Ag, -!-Pb,H30, etc.) iswidely used in the metallurgical industry as a means ofcontrolling iron, sulphate or alkalis in processing solutions.The principal application is for iron control in sulphate-basedhydrometallurgical zinc circuits[lJ although the technologyalso is being employed in copper and cobalt operations [2].In cupric chloride/ferric chloride leaching processes, jarositeprecipitation can be used for both sulphate and iron control[3]. The precipitation ofjarosite-type compounds from chloridesolutions is relatively straightforward provided that a separatesource of sulphate is available and the pH of the solution isnot too low [4]. Although alkalis are normally added to initiatejarosite precipitation for iron or sulphate control, it is alsopossible to add excess ferric ion to a sulphate solution with theaim of precipitating unwanted alkalis. The latter technique hasbeen employed for alkali removal from manganese sulphatesolutions [5J, and seems to be particularly effective for potas-sium control, with K levels < 10ppm being achieved readily.The advantages of jarosite precipitation include: the effectiveelimination of iron, sulphate or alkalis, low losses of sought-after divalent metals such as Zn, Cu or Mn, and the excellentsettling and filtration properties of the precipitates.
The jarosite formula can be represented schematically asMB3X2 Y6' where M is nominally monovalent, and B istrivalent. A number of substitutions have been demonstratedfor the monovalent M-site [6J and for the trivalent B-site [7].In addition, the coupled substitution of two divalent ions fora monovalent plus trivalent ion can occur under certaincircumstances [7J, and this effect has been illustrated mostextensively for Pb2+ + Cu2+ = M+ + Fe3+ [8J. Completesubstitution for the SO~- in the X-site has been reported forSeOi - and CrOi - [7J, but many of the common anions suchas MnOi - or TeOi - do not enter the structure to anysignificant extent. Very little work has been reported on
substitutions for OH- in the monovalent }:site, but it seemspossible to replace at least one of the OH- ions with F-.
Arsenic is a common impurity in metallurgical ores andconcentrates. Arsenic is present as arsenides, e.g. arsenopyriteFeAsS or cobaltite CoAsS, as sulphosalts, e.g. tetrahedrite-tennantite CU12(Sb,AS)4S13,and as a substitutional elementin some sulphides. During oxidative hydrometallurgical pro-cessing, at least part of the arsenic is oxidized either to arsenate(AsO~-) or to arsenite (As02 or AsO~-), with the extent ofreaction being notably high in 02-pressure leaching systems[9J and in ferric chloride leaching media [10]. Althoughthermodynamic considerations indicate that arsenate is thestable species, arsenite is extensively metastable in manyleaching systems [10, 11].
Despite the fact that arsenic is a common impurity inmany hydrometallurgical processing solutions, little has beenreported on the behaviour of arsenic species during jarositeprecipitation. Yaroslavtsev et al. [12J investigated the precipit-ation of both arsenate and arsenite with potassium jarositeformed at 90 DC and pH = 1.5. They observed that arsenatewas extensively precipitated with the jarosite, but that arsenitetended to remain in solution. Details of the testwork were notprovided and it was not demonstrated whether the arsenicspecies were structurally incorporated by substitution forsulphate in jarosite, or whether they were present as separatephases. Arsenic is often detected in commercial or pilot plantjarosite precipitates [9J, but the form of the arsenic is ill-definedand the range of precipitation conditions reported is generallyrestricted. Dutrizac and Jambor [13J recently presented somepreliminary findings on arsenic incorporation in jarositesformed over a broad range of conditions, and it was concludedthat the arsenic mostly was present as a separate phase.
Because of the importance of arsenic impurities in hydrome-tallurgical processing and the general lack of systematic dataconcerning the behaviour of this element during jarosite precipi-tation, the behaviour of arsenate and arsenite during theprecipitation of various alkali jarosites has been investigated.
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92 J. E. DUTRIZAC and J. L. JAMBOR: JAROSITE PRECIPITATION
Work was done in both sulphate and chloride media, and overthe range of variables likely to be encountered in hydrometal-lurgical processing. A temperature of 97 DCwas selected for thetest work as many hydrometallurgical processes ~re conductedat .....,100 DC. The objectives were to illustrate the generalbehaviour of arsenic during jarosite precipitation and to offersome commentary on the mechanism of arsenic precipitation.
EXPERIMENTAL
Reagent grade chemicals were used for all syntheses. Arsenatewas added as Na2HAs04' 7H20, KH2As04 or As20s; arsen-ite was added as NaAs02 or AS2°3, The form of arsenic usedwas dependent on the cation under investigation, the need tomaintain constant alkali concentration, etc. The jarosites wereformed simply by dissolving in water the appropriate sulphateor chloride reagents together with the arsenic, adjusting thepH with H2S04 or MgC03, and then heating the chargeto the reaction temperature. Unless stated otherwise, a 24-hretention time was used as this is known to give near-equilibrium conditions at the 97 DC temperature studied [14].Solid MgC03 was used to raise the pH since magnesium doesnot form an end-member jarosite-type compound, and alsobecause the solid carbonate reacts slowly enough to preventlocal over-neutralization and attendant iron hydroxide precipi-tation. The experiments were done in a 2-1 reaction kettle fittedwith titanium baffles. At the end of the reaction period, theslurries were filtered, and any material adhering to the vesselwas removed and also was filtered. The precipitates werewashed with 41 of hot water and were subsequently dried at110 DC. The solution compositions and test conditions generallybracketed the optimum range for jarosite precipitation asidentified in previous work [14].
All the precipitates were analyzed chemically, and all were-examined by Guinier-deWolff X-ray diffraction analysis toconfirm the presence of a jarosite-type compound and toidentify possible impurity phases. Guinier precision focussingcameras are particularly sensitive to impurity phases and, forexample, it has been demonstrated that as little as 0.25 wt %scorodite in sodium jarosite can be detected by this technique.Additional X-ray powder patterns of many of the precipitateswere obtained using a Debye-Scherrer camera of 114.6 mmdiameter, CoKcx1 radiation (). = 1.7889 A), and MgO as aninternal standard. Refinements of the data were done usingreported procedures [8J and assuming a hexagonal cell witha ~ 7 and c ~ 17A.
RESULTS AND DISCUSSION
Effect of arsenate concentrationFigure 1 illustrates the effect of the initial concentration of
dissolved Ass+ (added as Na2HAs04' 7H20) on the compo-sition of the sodium jarosite precipitate formed by heating to97 DC for 24h a 0.2 M Fe(S04)l.s-0.3 M Na2S04 solution ofinitial pH = 1.6. Previous work [14J has shown that suchconditions are near-optimum for the precipitation of alkalijarosites. In the absence of dissolved AsS +, a sodium jarositeis formed that contains ~3.8% Na, ~33% Fe and ~400/0
45
0.2M Fe3+,O.3 M Na2S04,97°C40 "'- pH= 1.6,24 h
"'-8"'"
"'"35 "0
00.........
III ----, '"<t.. --,~ •030en '"
~ " tV
'8 •C 25 .x~z.-zwu 20
/ o/oio.a:wa...-:I: 15 ,(!)
~OASO'w~
10
5
/17;---g---g- "loNe--g---[j--
aa 2 3 4 5 65+
DISSOLVED As (g / L )
Fig. 1. Effect of dissolved AsS + concentration on the composition ofthe sodium jarosite precipitate made at 97°C.
S04; the calculated formula is Nao.80Fe2.7s(S04h.00(OH)6.00.The difference between the measured sodium content and thetheoretical value of 4.7% Na is thought to be due to H3 °+
substitution for Na + in the sodium jarosite structure [15].Hence, the formula of the sodium jarosite is(Nao.80H300.20)1.00Fe2.78(S04h(OH)6' The slight deficiencyof iron seems to be characteristic of jarosite-type compounds,and the necessary charge neutrality is likely effected by theconversion of some OH- to H20. That is, the true formulais likely (NaO.80H3 00.20)1.00 Fe2. 78(S04h (OH)S.34(H20 )0.66'As the initial concentration of AsS + in solution increases, thearsenate content of the bulk precipitate also increases and ina nearly linear fashion. The presence of 5 gjI AsS + in thesynthesis solution generates a product containing more than25% As04, and this represents > 90% precipitation of theinitially dissolved arsenic values. As the As04 content of theprecipitate increases, the S04 content decreases in an inverselyproportional manner. The decline in Na follows the trend ofsulphate although S04 decreases more rapidly than Na. Forexample, on increasing the AsS + concentration from 0 to 5 gil,the S04 content of the precipitate decreases to 51 % of its initialvalue and the Na content declines to 570/0 of its initialconcentration. The iron concentration is little affected, anddecreases only slightly. Virtually identical results were obtainedwhen the experiments were repeated at pH = 1.4.
Figure 2 illustrates the relative partitioning of sulphate andarsenate between the solution and the precipitates made atpH = 1.6 and 97 DC. These particular experiments were doneusing a ferric ion concentration of 0.3 M and constant concen-trations of 0.05 M As04 and 0.6 M Na. The sulphate to arsenate
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0. 8 r------,,......-----,----,----r-----,
1. E. DUTRIZAC and 1. L. JAMBOR: JAROSITE PRECIPITATION 93
0.7
0.3 M Fe 3+ I 0.05 M As04 ,97°C
pH=I.6, l: No = 0.6 M
0.6
e 0.5..Joen~ •.0.4o~
en +<to
en<t 0.3
L--..J
0.2
M= 4.6 /
0.1
0.0 0.1 0.2 0.3 0.4 0.5
[ AS~:~04]SOLUTION
Fig. 2. Relative partitioning of arsenate and sulphate between thesolution and the sodium jarosite precipitate made at 97°C.
ratios were varied by using different concentrations ofNa2S04and NaN03, but with a total 0.6 M Na concentration. Nitrateion has little effect on jarosite formation. As the molar ratio ofAs04/(As04 + S04) in the synthesis solution increases, thecorresponding ratio in the precipitate increases systematicallyand nearly linearly. The dashed line on the figure representsthe ideal precipitation behaviour, and from this it is evident thatarsenic is significantly and selectively (m = 4.6) concentrated inthe precipitate. In fact, as noted above, more than 90% ofthe initial dissolved arsenic was precipitated from the moreconcentrated solutions under these synthesis conditions.
Potassium jarosite is the most stable member of the jarositefamily [2], and the effect of the initial concentration of As5+
(added as KH2As04) on the formation of potassium jarositeat 97°C is illustrated in Fig. 3. The solutions used for theseexperiments contained 0.2 M Fe(S04)1.5-0.3 M K2S04 atpH = 1.4; the total reaction period was 24 h. The resultsobtained are similar to those realized for sodium jarositeprecipitation (Fig. 1). In the absence of dissolved arsenic, anormal potassium jarosite showing minor hydronium substitu-tion for K + , and a deficiency of iron, is formed. Thecalculated formula for the end-member jarosite is(KO.87H300.13)l.ooFe2.45(S04h.oo(OH)6.00' Increasing con-centrations of dissolved As5+ result in a systematic increase inthe As04 content of the product, and an inversely proportionaldecrease in S04' The K content drops steadily although notas rapidly as S04, and the percentage of iron remains relativelyconstant.
Figure 4 illustrates the relative partitioning of sulphate andarsenate between the solution and the precipitates made fromthe K-bearing solutions at pH = 1.4 and 97 °e. Although theseprecipitates were made from solutions having a constant 0.2 M
40
35o'tlf'
IIIcrJ30(I)
A_ A_ A- A A •
A ---- ~A --A
A %Fe---A. -//...
Zl&J
~20l&Ja..
//
/0/
//0/
~/ %As04/
//
//0
/
Fig. 3. Effect of dissolved As5 + concentration on the composition ofthe potassium jarosite precipitate made at 97°C.
0.8...----------oy------------,
0.6 /-ms6.0~(5en
r-""""1
~c! en 0.4 •+ f/en 0<t
en<l
rlL...--J
0.2 i ~,I ~.- ~.----/ .----
OJ.Oi:::::---------L.--------~o 0.1 0.2
[As04 ]
AsO. +504 Solution
Fig. 4. Relative partitioning of arsenate and 'sulphate between thesolution and the potassium jarosite precipitate made in sulphate media
at 97°C.
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94 J. E. DUTRIZAC and J. L. JAMBOR: JAROSITE PRECIPITATION
17.0r----~---..------,---__.____-_____,Fe3 + concentration, the K concentration varied slightly assmall amounts of KH2As04 were added to the 0.3 M K2S04solution. As was the case for the synthesis of sodium jarosite(Fig. 2), arsenate is preferentially precipitated from the potass-ium-bearing solutions. In this instance, however, the molarpartitioning coefficient is slightly higher at 6.0 (cf. m = 4.6 forsodium jarosite precipitation, Fig. 2).
The behaviour of ammonium jarosite, which like sodiumjarosite also is widely used in the metallurgical industry, ismore similar to that of sodium jarosite than that of thepotassium member. When ammonium jarosite was precipitatedin the presence of Ass +, a composition curve similar to Fig. 1was realized.
The precipitates made in the presence of sodium sulphate(Figs 1 and 2) had the characteristic yellow colour of jarosite-type compounds, and all the precipitates filtered readily. X-raypowder diffraction analysis indicated only well crystallizedsodium jarosite. The high As04 contents of the precipitates,the linear As04/(As04 + S04) molar distribution curve, andthe powder diffraction data could be interpreted as indicatingAs04 substitution for S04 in the sodium jarosite structure:
NaFe3(S04h(OH)6 + AsOl- + H+
--+ NaFe3(S04)(As04)(OH)s . H20
+ SOI-. (1)
The tetrahedrally co-ordinated AsOl- ion would be isostruc-tural with SO~ - , and charge neutrality would be maintainedby conversion of one of the structural OH- ions to H20 asoccurs, for example, in the svanbergite (SrAI3(P04)(S04)(OH)6)-goyazite (SrAI3(P04h(OH)s' H20) mineral ser-ies. Although this type of reaction may occur to a limitedextent, it is thought for the reasons given below that thearsenate is present mostly as a discrete amorphous phase.
Firstly, the decrease in the Na content of the arsenate-bearing sodium jarosite (Fig. 1) is considerably greaterthan expected for the hypothetical compoundNaFe3(S04)(As04)(OH)s . H20; nevertheless, the possibilityof enhanced hydronium substitution for sodium as the arsenatecontent increases cannot be ruled out. Secondly, Mossbauerspectroscopy indicated the presence of two phases, each con-taining ferric ions. Although the room temperature spectrumindicated only one species for the precipitate containing ~ 27%As04 (Fig. 1), the more accurate and informative spectrum at10 K revealed the presence of approximately equal amounts oftwo similar Fe3 +-bearing compounds. Only one of the spectrawas characteristic of jarosite-type compounds [16]. Thirdly,detailed examination of the X-ray powder diffraction patternsprovided no evidence of the substitution of As04 for S04'Powder diffraction patterns of the various precipitates of Fig. 1were indexed assuming a hexagonal cell, and the calculated aand c parameters are illustrated in Fig. 5.
The unit cell parameters of the sodium jarosite, the onlyphase detectable, are plotted as a function of the molar ratioof As04/(As04 + S04) in the precipitate. There is no significantvariation of either a or c with increasing arsenate content, evenfor AsO 4/(AsO 4 + SO 4) molar ratios as high as ~ 0.5. Thelack of a significant and systematic variation of a and/or c withincreasing arsenate content strongly suggests that the sodiumjarosite is largely arsenate-free although this conclusion must
16.80.2 M Fe3+, 0.3M N02 5°4,97 °C
pH = 1.6
e-e-----e-e---
16.4 5-0 (504) - 1.47 AAs-O (As04)-1.67 A
04 -e-e-e-e-e---7.3~
7.1 L...--_------'- __ ---'- __ --'-- __ ...l..-_-----lo 0.2 0.4 0.6 0.8 1.0
[ AS~~;04 JFig. 5. Variation of the unit cell parameters of the sodium jarositemade at 97°C with increasing As04/(As04 + S04) mole ratio in the
original solution.
be viewed with some caution. The arsenate ion is larger thanthe sulphate (As-O bond length in As04 is 1.686 A whereasthe corresponding S-O bond length in S04 is 1.473 A [17J),but this substitution does not always result in significantlylarger unit cell parameters. For example, beudantite PbFe3(As04)(S04)(OH)6 has cell parameters of a = 7.32, c = 17.02 A(PDFI9-689); these parameters are only slightly greater thanthose of plumbojarosite Pbo.s Fe3(S04h(OH)6: a = 7.32,c = 16.90 A [6,8]. Although there is also a difference in theextent of Pb-site occupancy in beudantite and plumbojarosite,the significantly greater cell parameters expected for beudantiteare not observed. There does not seem to be any change in M-site occupancy in the alkali jarosite-arsenate systems undercurrent study.
X-ray diffraction analysis of the precipitates made from K-bearing solutions (Fig. 3) indicated some differences relative tothe analogous sodium system. Although the precipitates madefrom solutions containing < 3 gil Ass + (Fig. 3) showed onlyK-jarosite, those made from solutions initially having 3, 4or 5 gil Ass + indicated additional minor amounts of wellcrystallized scorodite FeAs04' 2H20. Presumably scorodite ispresent in all of the precipitates, but in some, the amountand/or crystallinity of the scorodite is too low to be detected.The unit cell parameters of the potassium jarosite remainedrelatively constant as the arsenate content of the precipitateincreased from 0 to ~ 250/0. The a parameter was constant at7.31 A, but the c value increased systematically from 17.06 to17.15 A. This may indicate a slight substitution of AsOl- forsoI - in K-jarosite. The results suggest that nearly all of thearsenate is precipitated as scorodite, and that arsenate isnot structurally incorporated to a significant extent in thepotassium jarosite.
Effect of reaction time
Figure 6 illustrates the effect of reaction time on the composi-tion of the precipitates made at 97 DC from solutions containing
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95
80
70
60at
C
50~>=.-0
4050a:Q.
30
20
10
00.8
45.-------,-------,r----,----,----.-----,
1. E. DUTRIZAC and J. L. JAMBOR: JAROSITE PRECIPITATION
40 r------r----,----r---.----,------,
40 •0.3 M F.e!+,0.3 M NaeS04' 3g/L AS8+
97°C, pH-I.G
••35 •
i-AA
30 --AA A
0II)<t
0'" 25 •enIf /~tSz 20.-zw0a:::w 0Q. 15 /.-:I:C>
W 0~10 0
0
5
.~--
%Na----....,--
0~-.w~...L----L----L.--~--~:__-~o· 2 3 6
TIME (h)
Fig. 6. Effect of reaction time at 97°C on the compositi?n of thesodium jarosite precipitate made from sulphate medIa.
OJ M Fe(S04)1.S-0.3 M Na2S04-3 gil Ass+ (as Na2HAs04)at pH = 1.6. The data clearly suggest the precipitation of twocompositionally different phases. The initial material to form(t .....•3 g) is rich in Fe and As04 (",40 % As04) but is deficientin S04 and especially in Na. As the reaction continues, theAs04 content drops from ",40 % to about 11 %, the S04content rises from'" 9 % to 32 0/0, and the Na content increasesfrom a near zero level to about 3 %. About 13 g of precipitatewere formed after 5 h of reaction. The chemical data suggest theinitial and rapid formation of a ferric arsenate-type compoundfollowed by the progressive, and somewhat slower, precipitationof sodium jarosite. Nevertheless, sodium jarosite was the onlyphase detected by X-ray diffraction.
Effect of initial solution pHJarosite-type compounds are formed in acid media, and
generally over a restricted pH range. If the pH is too low (< 1),reduced amounts of jarosite are formed; if the pH is toohigh (> 2), then other iron compounds with poorer filtrationproperties precipitate with the jarosite. Figure 7 illustrates theeffect of the initial solution pH on the mass and composition ofthe precipitates made from 0.3 M Fe(S04)1.S-0.3 M Na2S04-3 gil AsS + solutions at 97°C. The product-yield curve is typicalof jarosite synthesis at ~ 100°C when the pH is not controlledduring the course of reaction. There is a region at higher pHwhere the amount of precipitate is relatively independent of
35
o •en ,h--~---e--o---o-o---o---"""""- % Feet..30oenor;25z~ -0--0-_
~ 20 0 '0,cr '0~ ',PRODUCT
~ .5 ~Co:) \
\
; 10I=--_._-- ..•..--,,..-..•...--O-~---.;----% AsO•
YIELD
5
•\0\\\\ %Na
\0
1.4 1.2 1.01.8 1.6
pH
Fig. 7. Effect of initial solution pH on the composition of sodiumjarosite precipitated at 97 DC from 3 gjl AsS + solutions.
the initial acidity. In this region, the acid produced by hydrolysisof the 0.3 M Fe3 + outweighs the acid initially present insolution. The acid generating equation is:
Na2S04 + 3Fe2 (S04h + 12'H20 ~2NaFe3(S04h(OH)6+ 6H2S04• (2)
As the pH is lowered, the initial acidity becomes more importantrelative to the hydrolysis acid, and less jarosite is formed. Atsome point, the initial acidity becomes so high that the ironhydrolysis reaction (equation (2)) is entirely suppressed and noprecipitate is formed. Regardless of the initial solution pH,however, the composition of the product remains surprisinglyconstant. This consistency indicates that precipitation of theamorphous arsenate is affected by pH approximately to thesame extent as that of sodium jarosite. Consequently, thefraction of the total arsenic precipitated drops systematicallywith decreasing pH as shown in Table 1.
X-ray diffraction analysis of all the precipitates of Fig. 7indicated only sodium jarosite. Furthermore, there was no
Table 1. Effect of the initial solution pH on the fraction of :~senateprecipitated from 0.3 M Fe(S04)l.S-0.3 M NazS04-5 gil As solu-
tions at 97°C
pH Percentage AsS + Precipitated
1.8 911.7 771.6 741.5 681.4 541.3 391.2 301.1 10
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96
55
50
45
40
•0III
35~o·en
30i0z
25~zwU0:: 20wa..~
15:I:~w:t
10
5
J. E. DUTRIZAC and J. L. JAMBOR: JAROSITE PRECIPITATION
0.2 0.3 0.4[Fe!+] (moI/L)
Fig. 8. Effect of Fe3 + concentration on the composItIOn of theprecipitates formed at 97°C.
0.2 M N02 S04 I 3g/L As5+
pH=I.5,97°C
o
£t=1 · · %F.
0.1 0.5
significant or systematic variation of the unit cell parametersas the pH of the synthesis medium varied; at pH = 2.0, a = 7.35,c = 16.66A, and at pH = 1.2, a = 7.33, c = 16.66A. The X-raydiffraction results suggest that the arsenate is precipitated asan amorphous compound, and that the crystallinity of thearsenate compound at 97 DC is not affected by pH variationsin the range 1- 2.
The effect oj the Jerric ion and alkali concentrations
The effect of the Fe3 + concentration on the composition ofthe precipitates formed at 97 DC from solutions containing0.2 M Na2S04-3 gjl Ass+ at pH = 1.5 is illustrated in Fig. 8.It is clear that ferric ion concentration exercises a majorinfluence on the relative precipitation of jarosite and thesuspected arsenate phase. In the absence of dissolved Fe3 +, noprecipitate is formed. As the iron concentration increases, thetotal weight of the precipitate also increases linearly. Thisbehaviour is expected because there is a stoichiometric excess ofsodium to form sodium jarosite for all of the iron concentrationsinvestigated [14]. In dilute (0.03 M Fe3 +) iron solutions, theproduct is greenish yellow and contains 24.3 % Fe and 64.3 0/0
As04, but negligible amounts of sodium or sulphate. Althoughamorphous to X-rays, the product is near scorodite in composi-tion (FeAs04· 2H20: Fe 24.4 %, As04 60.7 %, H20 14.8 %),and is probably best considered as "amorphous scorodite". Asthe iron concentration of the solution increases, there is adramatic decline in the As04 content of the precipitate, and acorresponding increase in the S04 and Na contents. Thisindicates that the amount of amorphous "scorodite" is decreas-ing relative to sodium jarosite.
5O,.......-----~----_r_----_.----......,
40
0.3 M Fe3+, 4 g/ L As~+ (As20e)pH-I.5,97°C,24h
45
10
°'--)""10---=0---=0--0/05°4
~~35oC/)
af•.30oz~ffi 25()a::lLJQ.
~20C)
W~15
%Fe••••• --J.--=A=-----=A----A--Ir--A_
~ 0 ° 0
'\$I~.:.".-.-.'-_.------.--- .% As04
5%Na
•• 1-__.--.--.--.--.-••° •° 0.1 0.2
[Na25~] (moI/L)0.3 0.4
Fig. 9. Composition of the sodium jarosite precipitates formed at 97°Cfrom solutions containing various concentrations of Na2S04•
Figure 9 shows the vanatlon in the composItIon of theprecipitates made from solutions having various initial concen-trations of Na2 S04. All tests were done at 97 DC for 24 handutilized solutions containing 0.3 M Fe(S04)l.s-4 gil Ass+ (asAs20S) at pH = 1.5. In the absence ofNa2S04 an iron arsenatecontaining '" 38 °10 As04, 10 % S04 and 28 % Fe is formed.As expected, no sodium was detected in this precipitate. X-raydiffraction showed this compound to be amorphous, and thisobservation is consistent with the data reported above. As theNa2 S04 concentration of the solution increases, the Na contentof the precipitates rises rapidly to a value of '" 3 % Na at0.05 M Na2S04. A sodium sulphate concentration of 0.05 Mis approximately the stoichiometric concentration needed toform sodium jarosite from all the 0.3 M Fe3 + present. Highersodium concentrations have little effect on the composition ofthe product. The increase in Na is paralleled by an increase inS04 and a decline in As04. The composition of the precipitatesis nearly constant for Na2S04 concentrations >0.05 M. X-raydiffraction study of the precipitates made in the presence ofNa2 S04 indicated only sodium jarosite.
Similar experiments were carried out whereby the (NH4hS04 concentration of 0.3 M Fe(S04)l.s-4 gjl AsS + (as As20S)solutions was varied from 0 to 0.3 M. The compositions ofthe precipitates made from the ammonium-bearing solutionsparalleled those shown in Fig. 9. In the absence of(NH4hS04'the precipitate contained'" 31 % Fe, 42 % As04 and 8 % S04.As the (NH4hS04 concentration increased, the ammoniumcontent of the product increased to about 0.05 M (NH4h S04,but thereafter remained nearly constant. Although the Fe
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50 ..---~----r----,;---.---.-----r--.-----"'"
J. E. DUTRIZAC and 1. L. JAMBOR: JAROSITE PRECIPITATION 97
450.5 M FeCI3, 3 M NaCl, 0.2 M Na2S04
97°C,pH=1.0
'f"40oVI«J 35(J)
.i030
:2:t-
~ 25u0:W
~ 20:I:C)
~ 15
•
o
10
5
2 34 5 6 7 8
DISSOLVED AS6+( 9 / L )
Fig. 10. Effect of the As5 + concentration on the composition of thesodium jarosite precipitates formed from chloride media at 97°C.
content remained nearly constant, the S04 content increasedsharply and the As04 content decreased in an inverse manner.For synthesis solutions containing 0.2 M (NH4h S04, theprecipitate contained ~ 2.5 0/0 NH4, 32 0/0 Fe, 34010 S04 and10010 As04·
Behaviour of arsenate (Ass + ) in chloride solutions
It is well established that jarosite-type compounds can beprecipitated from chloride solutions, provided that a separatesource of sulphate is available and that the pH is closelyregulated [3,4]. The effect of arsenate concentration (asNa2HAs04) on the composition and properties of the precipi-tates formed at 97°C from 0.5M FeCI3-3M NaCI-0.2MNa2S04 solutions at pH = 1.0 was studied, and the chemicaldata are presented in Fig. 10. In the absence of dissolvedarsenic, a sodium jarosite was formed that analysed 4.04 0
/0
Na, 32.8 0/0 Fe and 39.8 % S04' Its calculated formula is(Nao.8SH3 0o.ls)1.00Fe2.84(S04h.oo(OH)6.00 although thisrepresentation ignores the minor conversion of OH to H2°tomaintain charge neutrality resulting from the slight deficiencyof Fe. As the concentration of As04 increased in the solution,the products obtained became progressively richer in As04and deficient in S04; the Fe content decreased slightly and theNa content dropped appreciably. For example, in the presenceof 4 gil Ass + in the chloride medium, the product contained2.47 % Na, 27.3010 Fe, 22.1 0/0 S04 and 26.4 0/0 As04. Compari-son with Fig. 1 indicates that, chemically, Ass + behaves simi-larly in either sulphate or chloride media.
A major difference between the two systems, however, is inthe crystallinity of the iron arsenate precipitate. In the presenceof sodium ion at 97°C in sulphate media, the iron arsenateprecipitate is amorphous. In the corresponding chloride system,
Table 2. X-ray diffraction data and chemical analyses for precipitatesmade from chloride solutions containing As5 +
As5 + concentrationof solution (gil)
% As04 inprecipitate X-ray data
0.000.100.250.500.751.01.0
0.000.370.741.431.852.602.88
Na-jarositeNa-jarositeNa-jarositeNa-jarositeNa-jarositeNa-jarosite
Na-jarosite + tracescorodite
Na-jarosite + minorscorodite
1.0 (?) 7.47
the arsenate-bearing precipitate is readily identifiable as scorod-ite (FeAs04' 2H20) by X-ray diffraction. Furthermore, theintensity of the scorodite lines increased systematically withincreasing amounts of As04 in the precipitate. Table 2 presentssome of the Guinier X-ray diffraction data obtained from theseprecipitates. Precipitates containing up to 2.60wt 0/0 As04consist only of sodium jarosite having a = 7.32 and c = 16.61A.A trace of scorodite was present in the precipitate containing2.88 0/0 As04 and a minor amount of scorodite was detectedin the product having 7.47 % As04. There was no variationin either a or c of the sodium jarosites formed in this series oftests. Separate tests were done whereby synthetic scorodite wasmixed with sodium jarosite and subsequently analysed byGuinier X-ray diffraction. In those experiments the equivalentof 0.60wt % As04 was detected on the Guinier pattern as adistinct trace, and 1.81 0/0 As04 gave strong scorodite lines.The scorodite formed in chloride media (Fig. 10 and Table 2)is well crystallized as is evident from the sharpness of thepowder diffraction lines. Scorodite in the precipitates havinglower As04 contents presumably also is well crystallized, andthus the lack of detection of scorodite may be indicative of alimited solid solution of As04 in sodium jarosite. Assuming adetection limit of ~0.60 0/0 As04, the data of Table 2 suggestsa solubility limit of ~ 2 0/0 As04. That the substitution of thisquantity of As04 does not affect the cell parameters of thesodium jarosite is unexpected, and this aspect will be discussedin greater detail in a subsequent paper. Although the reasonsfor the crystallization of scorodite in chloride solutions and theformation of amorphous iron arsenate in sulphate solutionsunder similar conditions are not known, the similarities inprecipitation behaviour in the two systems strongly suggestthat the amorphous arsenate perceived in sulphate media at97°C is chemically similar to scorodite.
Behaviour of arsenite ( As3 + ) in sulphate and chloride media
Figure 11 illustrates the effect of the concentration of As3 +
on the composition of the precipitates made at 97°C from0.3 Fe(S04)l.s-0.3 M Na2S04 solutions at pH = 1.5. Theexperiments were run for 24h under a nitrogen atmosphere toprevent air oxidation of the arsenic. The As3 + was added tothe solution as NaAs02. It is evident that the composition ofthe precipitate is independent of the As3 + concentration ofthe starting solution, and that the measured compositioncorresponds closely to that of sodium jarosite. The arseniccontent of the precipitate, arbitrarily expressed as As03,
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98
45
40
35..,0enex..
30en.iC 25z~zw 20ua:wQ.
~15z
~w~
10
5
00
J. E. DUTRIZAC and J. L. JAMBOR: JAROSITE PRECIPITATION
55 r----,----.---.-------r----,---~--y__-____,
%504H=--....-ot:j------'tt--------u---o- 500.3M Fe(504)1.5 ,O.2MK2S04, pH: 1.5
97°C,24 h
45
•%504
%Fe --0--0--0 --0--0--0--0-
O.3M Fe3+,O.3 M Na~S04
pH=I.5,97°C
2 3 4 5DISSOLVED As5+(g/L)
Fig. 11. Behaviour of As3 + during sodium jarosite precipitation at97°C in sulphate media.
6
increases steadily with increasing amounts of As3 + in solution,but the maximum "As03" content of the solid is always<0.60/0. Clearly, negligible amounts of As3 + are precipitated;even the limited amount of As precipitation observed probablyarises either from a minor amount of As5 + in the arsenitereagent, or from the gradual oxidation of As3 + by ferricsulphate [18]. That is, the minor amounts of arsenic areprecipitated as arsenate and not as arsenite. To investigate theeffect of possible air oxidation of As3 +, the above experimentswere repeated, but with the vessels open to the air. Virtuallyidentical results were realized, and the "As03" contents of theproducts were <0.60/0, thereby indicating that air oxidationof As3 + was not a significant factor under the conditions usedfor these tests. Potassium jarosite is the most stable of thejarosite compounds, and under a given set of conditions itusually will incorporate more of a given impurity than sodiumjarosite [7]. Accordingly, a systematic series of experimentswas done whereby potassium jarosite was precipitated at 97°Cfrom pH = 1.5 solutions; these solutions contained 0.3 MFe(S04)1.5-0.2 M K2S04 and As3+ concentrations (added asAS203 in a small amount of KOH solution) ranging from 0 to7 gjl. The results (Fig. 12) are similar to those realized forsodium jarosite under similar conditions (Fig. 11). The nearlyconstant quantity of precipitate obtained was found by X-raydiffraction to consist only of (potassium) jarosite in whichthe a or c parameters remained constant despite increasedconcentrations of arsenic. Chemically, a "normal" potassiumjarosite is formed that contains'" 7.5 % K, 30 % Fe and 41 %
S04' The "As03" contents of the precipitates are consistentlyless than 0.3 wt %. These data, together with those of Fig. 11,
~ %~i.:.o --e--e--e--e--e--e--e-~•...ffi 25ua:~~ 20C)W~
15
10%K
--0----=°"---.0--0--0--0--0-
5
0•.....---=.J===--'==w===4J===-L==:.e===.t--==---lo 2 3 4 5 6 7 8
DISSOLVED As3+ (gIL)
Fig. 12. The effect of As3+ on the composition of the potassium jarositeprecipitate made at 97°C from sulphate media.
indicate that As3 + is not precipitated significantly duringjarosite formation, and this conclusion is in agreement withthe observations of Yaroslavtsev et al. [12]. The charge andco-ordination of the As02 or AsO~ - ions make them unlikelyreplacements for SO~ - in the structure of jarosites.
Precipitation of sodium jarosite in the presence of As3 + inchloride media gave significantly different results (Fig. 13).These precipitates were made by heating 0.5 M FeC13-3 MNaCI-0.2 M Na2S04 solutions at pH = 1.0 for 24 h at 97 ccin a vessel open to air. As the As3 + concentration of thesolution increases, arsenic in the precipitate (reported as As04
for reasons noted below) increases significantly, and the sulph-ate content decreases in an inverse manner. The iron contentdecreases slightly and there is an important reduction in theNa content. The mass of the precipitate increases gradually asthe As3 + concentration of the solution increases. The data aresomewhat similar to those realized using As5 + in the chloridesynthesis solution (Fig. 10) except that the results, especiallythose for S04 and As04, are more scattered when the arsenicis added as As3 +.
X-ray diffraction analysis indicated minor to major quantitiesof scorodite in the precipitates made from solutions initiallycontaining >0.5 gjl As3 +. Because a chloride system was used,the scorodite was well crystallized. The precipitate made from0.5 gil As3 + solution contained 0.57 % As04 and consisted ofsodium jarosite only. The precipitate made from 1.0 gil As3 +
solution contained 2.88 wt % As04 and contained a trace of
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50,....-- ---r-------r----,...---..,..----,-------r---r--......,
1. E. DUTRIZAC and 1. 1. JAMBOR: JAROSITE PRECIPITATION 99
45 O.5M FeC13,3.0M NoCI,O.2M No2S04
97°C,pH=1.0
••
b..;
\.1.. % AS04;3Z % Fe.-z1LIU --- % 504a:: • •IJJ 0lL..-:I: 0C)IJJ 15~
10
0
5
2 3 4 56 7 8DISSOLVED As3+(g/U
Fig. 13. The influence of As3 + on the composition of the sodiumjarosite precipitates made at 97°C from chloride media.
scorodite. As noted above, 2.88 % AsO 4 if present as wellcrystallized scorodite, would give strong lines on the GuinierX-ray pattern. The conclusion is that part of the As04 may bepresent in solid solution in the jarosite structure.
The presence ofscorodite (FeAs04' 2Hz 0) in the precipitatesmade from solutions initially containing only As3 + suggeststhe rapid oxidation of As3 + to Ass + in chloride media. Infact, ion chromatographic analysis [11,18] of the precipitatesdissolved in hydrochloric acid indicated only Ass + and theabsence of As3 +. Unlike sulphate solutions where As3 + is veryslowly oxidized by ferric sulphate, chloride solutions providea suitable medium for the relatively rapid oxidation of As3 +
[11].
As3 + + 2FeCl3 ~ Ass + + 2FeClz + 2CI-. (3)
Presumably, the arsenite added to the synthesis solutionis rapidly oxidized to arsenate which then precipitates asFeAs04' 2Hz 0 (scorodite) with the sodium jarosite. Variationsin the oxidation rates are likely responsible for the considerablescatter of the As04 contents of the precipitates, and theresulting variations in sulphate. Although the arsenic is readilyprecipitated in chloride media, there is no indication that As3 +
(arsenite) itself is precipitated with or in the jarosite.
Arsenate distribution during jarosite precipitation
The above data indicate that extensive co-precipitation ofarsenate (as crystalline scorodite or amorphous iron arsenatechemically similar to scorodite) occurs during jarosite for-mation. The extent of arsenate precipitation has been shownto be highly dependent on the Ass + concentration, the alkaliand ferric ion' concentrations, the solution pH, etc. To givesome indication of the general deportment of arsenate undernear-optimum conditions for jarosite formation, however, a
series of experiments was done at 97°C using pH = 1.5 solu-tions containing 0.3 M Fe(S04)1.S-0.3 M Naz S04 and variousconcentrations of Ass +. The initial and final solution volumesand ,AsS+ concentrations were determined together with themass and As04 content of the dried precipitates; in most casesthe total arsenic accountability was better than 900/0 .
Figure 14 illustrates the effect of the Ass + concentration ofthe initial solution on the relative distribution of Ass + betweenthe precipitate and the final solution. Although there is consider-able scatter, the results indicate that in dilute arsenic solutions(AsS + < 0.4 gil), about one-quarter of the arsenic is precipitatedwith the sodium jarosite during the 24-h reaction periodsemployed. As the concentration of Ass + in the initial solutionincreases, the fraction of arsenic co-precipitated with the sodiumjarosite also increases. For dissolved arsenic concentrations> 5 gil, about 90 % of the arsenate is precipitated with the
jarosite. Although jarosite precipitation could be useful inarsenic control in a hydrometallurgical circuit, it does not yieldreally low arsenic concentrations in the final solution. Forexample, in many of the tests involving even modest (-- 1 gilAs04) arsenic concentrations, the final arsenic concentrationwas commonly several hundred mg/l; these concentrationsarise, at least in part, from the higher terminal acidities ( -- 0.3 M)caused by hydrolysis acid generated during the reaction. Highacidities are known to increase the solubility of scorodite [19]and, of course, the amorphous iron arsenate phase will have ahigher solubility than well crystallized scorodite.
CONCLUSIONS
The behaviour of As3 + and Ass + during alkali jarositeprecipitation has been investigated over a wide range ofsynthesis conditions. Although arsenate is readily precipitatedwith the alkali jarosites, it seems to be present mostly as aseparate phase. There is no indication of extensive AsO~-substitution for S04 in the jarosite structure although a limiteddegree (--20/0) of As04 substitution is suggested. Duringsodium or ammonium jarosite precipitation in sulphate mediaat 97°C, an amorphous arsenate phase, chemically similar toscorodite FeAs04' 2Hz 0, is formed. In such systems, arsenateis selectively precipitated relative to sulphate. During potassiumjarosite precipitation from sulphate media at 97°C, crystallizedscorodite is formed from arsenic-rich solutions but an amorph-ous arsenate is produced from dilute media. Again, arsenate isselectively precipitated relative to sulphate. X-ray diffractionstudy of the jarosites showed little variation of either the a orc parameters with increasing arsenate concentrations in theprecipitate, and this suggests that the extent of arsenatesubstitution in these species is minimal. It is shown that theamorphous arsenate phase or scorodite precipitates morerapidly than jarosite-type compounds; initial precipitates aretherefore enriched in AsO 4 and are deficient in alkalis andS04' Solution acidity seems to affect the precipitation of thejarosite and arsenate phases equally at 97°C; consequently, thecomposition of the precipitates does not vary significantly forinitial pH variations in the range 1-2. The total mass ofprecipitate formed, however, decreases with increasing acidconcentrations, and hence, less As04 is precipitated from the
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100 J. E. DUTRIZAC and J. L. JAMBOR: JAROSITE PRECIPITATION
140
120 0.3 M Fe{S04) us' 0.3 M NQ2S04, pH = 1.5
~ 100 •w •Cf) .~a:::<t-J 80 ~oo • •<t I PRECIPITATEz o e •(5
~ ~~80a: 0 I0 60 •t- o"j •z
wu ,0:: 40 0 @w ..•..•••..a.. o • • • g,,@y. • I '-..
20 • •O~AL SOLUTION
00
0 2 3 4 5 6 7 8 9 10 IIDiSSOLVED As!S+ ( g/ L )
Fig. 14. Relative partitioning of As5 + between the solutions and the precipitates formed at 97°C fromsulphate solutions.
more acidic environment. Both ferric ion and alkali concentra-tions affect the relative extent of precipitation of the arsenatephase, whose precipitation is favoured by low concentrationsof either ferric ion or alkali sulphate. The crystallinity of thearsenate phase, however, is not influenced by such concentra-tion variations. Arsenite is not precipitated during jarositeformation in sulphate media at 97°C, and there is no indicationof arsenite incorporation in the jarosite structure. Partialoxidation of the arsenite to arsenate, however, leads to arsenicco-precipitation with jarosite-type compounds.
Arsenate is readily precipitated with alkali jarosites madefrom chloride media at 97°C and the degree of precipitationis similar to that observed in the corresponding sulphatesystems. A notable difference, however, is that scorodite is wellcrystallized in chloride media. Guinier X-ray results obtainedfrom the jarosite-scorodite precipitates formed in chloridemedia indicate that '" 2 wt % As04 substitution occurs insodium jarosite, but this observation requires confirmation.Arsenite compounds are not precipitated during jarosite for-mation in chloride media, but because As3+ is rapidly oxidizedto Ass + by FeCl3 media, extensive arsenic precipitation doesoccur.
During alkali jarosite formation at 97°C, As04 precipitationincreases from '" 25 % in dilute solutions to ",90 % forsolutions containing > 5 gjl Ass +. The extent of arsenateprecipitation depends on many factors, however, and consider-able variation in the amount of arsenic precipitated can beexpected. Because most of the arsenate precipitated occurs ascrystalline or amorphous FeAs04 . 2Hz 0, the behaviour of thiselement in jarosite storage ponds might differ significantly fromthat of the jarosite itself. In particular, the oxidizing acidicconditions necessary to stabilize the jarosite could well resultin the progressive dissolution of the arsenic.
Acknowledgements- The authors recognize the assistance of O.Dinardo and D. J. Hardy with the precipitation studies and the helpof E. J. Murray and P. Carriere with the X-ray determinations.
REFERENCES
1. V. Arregui, A. R. Gordon and G. Steintveit, The jarosite process-past, present and future, in Lead-Zinc- Tin 'SO (edited by J. M.Cigan, T. S. Mackey and T. J. O'Keefe) pp. 97-123. TMS-AIME,Warrendale, PA (1979).
2. J. E. Dutrizac, Jarosite-type compounds and their application inthe metallurgical industry, in Hydrometallurgy Research. Develop-ment and Plant Practice (edited by K. Osseo-Asare and J. D. Miller)pp. 531-551. TMS-AIME, \Varrendale, PA (1982).
3. G. E. Atwood and R. W. Livingston, The CLEAR process-aDuval Corporation development, paper presented at the AnnualConference of Gesellschaft Deutscher Metallhutten und Bergleute,Berlin, September 26-29, 1979.
4. J. E. Dutrizac, Jarosite formation in chloride media, Proc. Australas.Inst. Min. Metall. 278,23 (1981).
5. P. D. Bowerman, T. W. Clapper and W. G. Laughlin, Manufactureof manganous sulphate solutions, U.S. Patent 4,489,043, Dec. 18,1984.
6. J. E. Dutrizac and S. Kaiman, Synthesis and properties of jarosite-type compounds, Can. Mineral. 14, 151 (1976).
7. J. E. Dutrizac, The behaviour of impurities during jarosite precipit-ation, in Hydrometallurgical Process Fundamentals, (edited by R.G. Bautista), pp. 125-169. Plenum, New York (1984).
8. J. L. Jambor and J. E. Dutrizac, The synthesis of beaverite, Can.Mineral. 23, 47 (1985).
9. G. B. Harris, S. Monette and R. W. Stanley, Hydrometallurgicaltreatment of Blackbird cobalt concentrate, in HydrometallurgyResearch, Development and Plant Practice, (edited by K. Osseo-Asare and J. D. Miller), pp. 139-150. TMS-AIME, Warrendale,PA (1982).
10. J. E. Dutrizac and R. M. Morrison, The leaching of some arsenideand antimonide minerals in ferric chloride media, in Hydrometal-lurgical Process Fundamentals, (edited by R. G. Bautista), pp. 77-112. Plenum, New York (1984).
11. L. K. Tan and J. E. Dutrizac, Determination of As(III) andAs(V) in ferric chloride-hydrochloric acid leaching media by ionchromatography, Analyt. Chem. 57, 1027 (1985).
12. A. S. Yaroslavtsev, L. S. Getskin, A. U. Usenov and E. V. Margulis,Behaviour of impurities when precipitating iron from sulphate zincsolutions, Tsvet. Metally 16(4),41 (1975).
13. J. E. Dutrizac and J. L. Jambor, Impurity control during jarositeprecipitation, in Proc. 15th Ann. Hydrometal. Meeting, ImpurityControl and Disposal, (edited by A. J. Oliver), paper 23. CIM,Montreal (1985).
14. J. E. Dutrizac, Factors affecting alkali jarosite formation, Metall.
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J. E. DUTRIZAC and J. L. JAMBOR: JAROSITE PRECIPITATION
Trans. 148, 531 (1983).15. J. A. Ripmeester, C. I. Ratcliffe, J. E. Dutrizac and J. L. Jambor,
Hydronium ion in the alunite-jarosite group, Can. Mineral. 24,435(1986).
16. A. Leclerc, Room temperature Mossbauer analysis of jarosite-typecompounds, Phys. Chern. Minerals 6, 327 (1980).
17. M. Boubia, M. T. Averbuch-Pouchot and A. Durif, Ordered As04
101
and S04 tetrahedra in diammonium trihydrogen arsenate sulfate,Acta Cryst. C41, 1562 (1985).
18. L. K. Tan and J. E. Dutrizac, Determination of arsenic (III) andarsenic (V) in ferric sulphate-sulphuric acid leaching media byion chromatography, Analyt. Chern. 57, 2615 (1985).
19. P. M. Dove and J. D. Rimstidt, The solubility and stability ofscorodite, FeAs04' 2H20, Am. Mineral. 70, 838 (1985).