Biopolymer Stabilization for Mine Tailings Dust ControlRui Chen (Graduate Student), Mark Gregory (Undergraduate Student), Lianyang Zhang (Advisor)

Department of Civil Engineering and Engineering Mechanics, The University of Arizona

Background Why Use Biopolymer? Preliminary Results (Cont.)

Preliminary Results

Preliminary Results (Cont.)

Conclusions

Research Approach

The mining industry produces significant amount of mine tailings (MT) every year. Most of the MT are disposed of in on-site impoundments behind engineered earth and rock dams, which leads to different environmental and safety concerns. MT are susceptible to wind erosion, especially in arid and semiarid regions. The fugitive dust can reduce the visibility along nearby roads, degrade air quality in the vicinity, and contaminate soils and surface water. The failure of tailing dams or impoundments can cause large amount of contaminated liquid and slurry released into the environment, resulting in pollution and loss of lives and properties.

Different methods have been attempted to stabilize MT in order to improve the impoundment stability and the erosion resistance. Ordinary Portland cement (OPC) has been used to stabilize tailings dams. However, OPC is an energy-intensive material and its production generates significant amount of carbon dioxide (CO2). Conventional methods to reduce wind erosion includes using physical covers such as gravel, synthetic materials, or topsoil from nearby site, using chemical stabilizers such as lignin sulfonate or polyacrylamide copolymers (PMA), and phytostabilization by introducing particular plants. However, all these methods have limitations. For example, the transportation of soil from nearby site may be expensive or the soil may simply not be available. Chemical stabilizers are generally expensive and some of them may have negative impact on the environment. MT usually show acidic pH and contain no organic matter, making them unsuitable for plants growing. The physical covering and phytostabilization methods are only applicable to MT impoundments after closure. Therefore, there is an urgent need for developing an environmentally-friendly and cost-effective technology for stabilization of MT.

At the University of Arizona, an extensive research program is being conducted on utilization of biopolymers to stabilize MT so that the impoundment stability and the erosion resistance are improved. Biopolymers are considered to be environmentally friendly because of their biodegradability and non-toxicity. The poster presents the preliminary results obtained so far.

Inclusion of either xanthan gum or guar gum increases the undrained shear strength of MT.

MT treated with xanthan gum or guar gum show obvious improvement in water retention capacity as indicated by the decreased speed of water loss.

MT treated with xanthan gum or guar gum show obvious improvement in dust resistance as indicated by the decreased weight loss of dry MT samples in the wind tunnel tests.

Biopolymer possesses long chains which form crosslinking networks bridging the MT particles; the presence of numerous hydroxyl groups and polar groups is beneficial to the formation of numerous hydrogen bonds and ionic bonds that strengthen the MT.

Increase of Undrained Shear Strength

Biopolymer concentration versus undrained shear strength at water content w = 30% and viscosity of biopolymer solution.

Water retention properties of MT samples treated with xanthan gum, guar gum and soil-sement solution at different concentrations

Wind Tunnel Tests

Weight loss of dry MT samples treated with xanthan gum, guar gum and soil-sement solution at different concentrations

ESEM Imaging

AcknowledgementThe research is supported by Freeport-McMoRan Copper & Gold Inc., Arizona. The Midwest Industrial Supply, Inc. provided the Soil-Sement sample used in this study.

ESEM images of MT treated with (a) Guar gum; and (b) Xanthan gum

innocuous

(a) (b)

Underlying Mechanisms of Improvement

HOHO

CH2

OO

O

HO

NH2

O

OH

OH

abundantly available

Xanthan gum

Guar gum

Ionic bond

Hydrogen bond

MT particle

Strength TestsStrength Tests

Macro-Scale StudyMacro-Scale Study

Wind Tunnel TestsWind Tunnel Tests

Durability TestsDurability Tests

Moisture Retention Tests

Moisture Retention Tests

ESEM ImagingESEM Imaging

Micro/Nano-Scale Study

Micro/Nano-Scale Study

XRD CharacterizationXRD Characterization

AFM NanoindentationAFM Nanoindentation

BET AnalysisBET Analysis

DEM SimulationsDEM Simulations

Development of a “Recipe”

0

1

2

3

4

5

6

7

8

9

We

ight

lost

(g)

0.3%

0 %

0.5%

0.8%

Xanthan gum

0.3%

0.5%

0.8% 3.8%1.9%

Guar gum

Soil-sement

7.6%

Water Retention Tests

biodegradable