aac_sheb_000111

8/11/2019 AAC_SHEB_000111

1/5

Issued on behalf of the Group Technical Director

This bulletin is published for general information and is not intended as professional advice. As every

situation depends on its own peculiar facts and circumstances, specialist advice should be obtainedwhere required.

ATD, VOHE Tel: +27 11 638 3045Administrative Contact: 5

thFloor, 45 Main Street Fax: +27 11 638 2610

Marshalltown, Johannesburg e-mail: [email protected]

1

Safety, Health & Environment Bulletin

May 2002 S111/2002

XANTHATE REAGENT:CONTROL OF RISKS ASSOCIATED WITH STORAGE AND USE

1 Introduction

Large quantities of various xanthate compounds are widely used in the Anglo American PlcOperations as collectors in sulphide flotation. Incidences have been recorded involvingaccidents associated with xanthate, notably an incident during August 2000 involving anexplosion at Amandelbult, but also in various literature.

The purpose of this bulletin is to highlight the risks associated with the use and storage ofxanthate and to reiterate methods for the control of these risks.

This bulletin is based on a detailed report on the subject prepared by the Anglo TechnicalDivision (Reference 1). (AAC_SHEG_000111)

2 Physical and Chemical Characteristics of Xanthate

Xanthates are delivered to operations as solids (pellets or powder) in drums or bulk bags,or in liquid form by bulk road tankers, depending the transport distances and the make-upfacilities on-site.

Solid xanthates are hygroscopic and may decompose in the presence of water to formcarbon disulphide, hydrogen sulphide, alcohols and hydroxides. These pose a risk to healthand of explosions and fire.

Liquid xanthates are considered to offer advantages of reduced fire risk, reduced operatorexposure and of consistent concentration delivered by suppliers. An excess of alcohol(ethanol, iso-butanol, iso-propanol amyl, etc.) and hydroxide are added in order to stabilizethe xanthate.

Occupational risk exposure scenarios are similar for both solid and liquid xanthates.However, risk exposures tend to be greater during the storage and mixing stages for solidxanthates.

Liquid xanthates are in themselves safe to handle, but have a limited shelf life and must beconsumed within a prescribed period (10 to 20 days).

8/11/2019 AAC_SHEB_000111

2/5







2

3 Risks Associated With Xanthates

Xanthates decompose on aging to form a number of byproducts, depending on the pH,temperature, etc. Fire and explosion risks associated with xanthate are, therefore, afunction of the breakdown of the product or un-reacted raw materials remaining in the

product.

Apart from the corrosive nature of sodium hydroxide and its effect on the skin the mainhazards are from carbon di-sulphide (CS2) and from the alcohol.

Carbon Di-sulphide

CS2is both a reagent in the manufacture, as well as a decomposition product of xanthates.It has an extremely low flash point (-27oC) and will start to burn with a spark or even a hotsurface in the presence of oxygen. CS2 is relatively insoluble in water and heavier thanwater and, therefore, it will collect in a layer under water. Spills or CS 2fires in containmentareas, e.g. bunded areas, are therefore easier to manage by the use of water. In otherareas the use of water to extinguish CS2fires may lead to spreading of the fire along the

water run-off routes.CS2 can be problematic with solid xanthates and storage, particularly if the packagingbecomes damaged. A number of xanthate (CS2) fires have been recorded in this regard.

Alcohols

Alcohols are both reagents used in the manufacture, as well as decomposition products ofxanthates. The specific alcohol depends on the xanthate species. The alcohols in questionrange from ethyl to amyl alcohol. They have low flash points (about 20oC to 50oC) and theyburn easily. They also have low vapour pressures and will form explosive mixtures with airin confined spaces (e.g. the vapour space above the xanthate solution in enclosed tanks).

The ignition of these vapours has also been recorded in the past.

Xanthate Manufacturing

Xanthates are reasonably stable when pure. The production of pure xanthates requirespure raw materials and then the reaction must also be driven to completion. This requiressophisticated process design and control of the manufacturing process which, in turn,influence the price and metallurgical efficiency of the product. Problems in the handling anduse of xanthate have arisen when:

Impure raw materials were used and side reactions occur which do not produce

Xanthate, but other unstable compounds.

The reaction between raw materials (CS2, sodium hydroxide and the alcohol) is not

driven to completion and significant amounts of the un-reacted materials are left in the

product. Intermediate, unstable thio compounds are also created and may be left in theproduct.

The product degrades into CS2and alcohol, either after manufacture in the solid form or

after dissolution before use.

Packaging, transport or storage results in contact of the product with air.

8/11/2019 AAC_SHEB_000111

3/5







3

4 Control of Xanthate Risks

On the basis of the risks highlighted above a number of control measures arerecommended by suppliers and end users for the safe handling of both solid and liquidxanthates (see reference report for further detail).

Isolation

The separation of people from the hazards of xanthate is achieved by locating xanthate off-loading, storage and mixing in a separately demarcated area/s of the plant. Theclassification of these areas must include standards pertaining to the selection ofinstrumentation and electrical equipment for use in hazardous locations (corrosion andfire/explosion risk).

Design and Engineering Controls

The objective of engineering controls is to minimise the hazards that arise during thedesign, construction and operation of facilities. Engineering controls that are generallyimplemented for xanthate storage and mixing facilities would include:

A comprehensive specification of the requirements for potentially flammable/explosive

areas such as solid xanthate storage areas and bulk liquid storages.

Comprehensive HAZOP during the design phase to unsure that necessary hazard

assessments are made during the early stages of design. The participation of experts in

the field and suppliers is necessary in these exercises.

Local mechanical forced ventilation systems to ensure that potential

flammable/explosive vapours are removed from the tanks and vented to atmosphere as

per the recommendations of the Material Safety Data Sheet.

Carbon steel is suitable for the fabrication of mixing and storage tanks.

Removal of all potential sources of ignition by appropriate selection of e.g. agitators,

mechanical seals and appropriately rated electrical equipment and instrumentation,including static electricity.

Comprehensive specification of mechanical, electrical and instrumentation equipment

for use in these areas.

Good ventilation of areas where solid xanthates are stored and mixed.

Bunding of the area to contain spillage.

Tanks to be kept cool to reduce the decomposition rate of xanthate and to limit the

alcohol vapour concentration. The temperature should preferably be below the flash

point of the alcohol used (note iso-butanol in SIBX has a flash point of 28 oC) and

above 5oC where xanthate will crystallise.

Storage and mixing tanks to be designed with conically shaped bottoms that slope

towards the transfer pump suction to facilitate removal of carbon di-sulphide and

sludges that may accumulate at the bottom.

Use of two storage tanks in the case of liquid xanthate deliveries for offloading into one

and drawing from the other. In this way either tank could be emptied and drained of

unwanted build up from time to time.

8/11/2019 AAC_SHEB_000111

4/5







4

Additional engineering controls in place at some Anglo sites include:

Deluge spray systems on storage and mixing tanks

Foam drop systems in the bunded areas.

Safe Work Practices

Safe work practices pertaining to offloading, storage and mixing of xanthate would include:

Restricted access to the area.

Storage of solid xanthates in cool dry places.

Prohibition of all ignition sources e.g. no smoking, no naked flames, etc.

Prompt cleaning of spills and maintenance of good house keeping standards.

Regular drainage and cleaning of tanks (note the requirements for working in confined

spaces and associated risk).

Regular checks on the condition of equipment and maintenance of equipment and

components that may cause a source of ignition or spillage. Maintenance in particular isconsidered to be a higher risk and requires special attention.

Avoid dust generation during solid xanthate make-up.

Personnel must be trained and periodically retrained in the hazards associated with

xanthate and the required control procedures implemented.

In the event of an incident /explosion ensure that the area is made safe prior to

investigation. This should include the isolation of potential sources of ignition such as

the agitator.

Disposal

The requirements for the disposal of xanthate (solid or liquid) or degraded products,spillage, etc. will vary depending on the circumstances. All disposals require specialconsideration and reference must be made to the suppliers Material Safety Data Sheet.

Personal Protection

Appropriate personal protection is to be worn when working with xanthates. This equipmentwould include respiratory protection, gloves, Safety glasses/goggles and safety shoes ratedto withstand the chemicals involved.

Reference must be made to the manufactures Material Safety Data Sheet for thespecification of emergency treatment and first aid requirements. The facilities generally

specified for chemical installations in this regard should be adequate in most instances.

Reference

The Process, Health, Safety and Engineering Issues Related to the Storage and Use ofXanthates, I.D Ralston, ATD Report No. PRE-2002-003, May 2002 (available through theadministrative contact below).

8/11/2019 AAC_SHEB_000111

5/5

5

Disclaimer

As contributors of this information, Anglo American plc or any of its Groupcompanies or their servants, agents or contractors, (generally referred to as theCompany), are not responsible for any actions (or lack thereof) taken as a result ofthe information contained herein and the Company cannot be held liable for anydamages resulting from reliance on or use of this information. Without limiting theabove, as contributors, the Company shall have no responsibility for any act oromission of any other contributor.

It is recorded that this material is presented for information purposes only, in theinterests of sharing good practice. Whilst the information may be regarded asindicative of good practice, and effort has been made to ensure that it is accurate,

no representation or warranty, express or implied, is made as to the accuracy,currency or completeness thereof. It is provided solely on the basis that users willbe responsible for making their own assessments of the information. Users areaccordingly advised to obtain independent advice before acting on the informationcontained herein, and to take specific advice from a qualified professional whendealing with specific situations.

The Company will accordingly not accept any liability for any loss or damage of anykind whatsoever (including consequential loss), suffered by any person acting inreliance upon the information, howsoever such loss or damage may have beencaused or sustained. The Company expressly disclaims liability for any such loss ordamage. By accessing the information presented on the terms and conditions

indicated, the user hereby indemnifies and holds the Company harmless against allsuch loss or damage.

aac_sheb_000111

Documents