Day A. Mining chemicals hand book

Подождите немного. Документ загружается.

Circuit pH Decomposition Time

8.3 6 days

9.9 4 days

11.1 4 hours

11.8 2 hours

12.5 15 minutes

AERODRI 100 dewatering aid, when fed full strength, should be

preconditioned with the pulp for periods of up to 10 minutes to

optimize filter cake moisture reduction.

AERODRI 104 dewatering aid

AERODRI 104 has a lower viscosity, and is more readily dispersible,

than AERODRI 100 dewatering aid. It is preferred where precondi-

tioning with the pulp is limited and dilute feed solutions are not

practical. It may be applied full strength, as an aqueous solution up

to about 3% concentration, or as an aqueous dispersion at higher

concentrations up to about 17%. AERODRI 104 dewatering aid is

biodegradable and exhibits the same alkali tolerance as for AERODRI

100 dewatering aid.

AERODRI 200R dewatering aid

AERODRI 200R dewatering aid was developed for applications

where recirculation of residual product in the water supply system

is undesirable. AERODRI 200R dewatering aid is at least 95%

retained on the mineral solids, thereby minimizing any build-up in

a closed-circuit water system. It may be applied full strength in a

well-agitated system for adequate preconditioning with the pulp, or

as an aqueous dispersion of up to about 10% concentration to the

filter boot or further upstream from the filter.

Physical characteristics of AERODRI dewatering aids

100 104 200R

Appearance Clear to Slightly Hazy

————— colorless to light yellow liquid —————

Solubility in Water, 20°C 1.7% 3.0% Dispersible

Specific Gravity, 20°C 1.08 1.03 0.96

Viscosity @20°C (cps) 250 26 30

Flash Point °C (closed cup) 32 46 45

Freezing Point °C 4 -4 4

Flocculants and dewatering aids

199

AERODRI 1000 dewatering aid

AERODRI 1000 dewatering aid was developed for use in the

centrifugal dewatering of coarse clean coal (>0.5 mm), without atten-

dant foaming problems which could aversely affect subsequent

processing stages, such as the recovery of heavy media. Its use can

result in increased calorific value of the final coal product. This

allows increased recovery of coal without adversely affecting overall

calorific value of the final product. This also enables the processing

of raw coal feed which previously had too high a moisture content

in the final product. Use of AERODRI 1000 at one coal processing

operation enabled the elimination of thermal drying, previously

required, with substantial cost savings.

AERODRI 1000 dewatering aid should be applied by spray nozzles

to the oversize coal product discharging from sieve bends or vibrating

screens, which feed the centrifuge dewatering unit. It should be

diluted at least 100:1 before spray application. This can be accom-

plished by feeding AERODRI 1000 dewatering aid through an eductor

into the water line feeding the spray nozzles, with sufficient water

flow to achieve the necessary dilution ratio.

Physical characteristics

AERODRI 1000 dewatering aid

Appearance Clear, pale yellow liquid

Solubility in Water Dispersible with vigorous agitation,

100-1 dilution preferred.

Specific Gravity 0.93 @ 20°C

Flash Point (closed cup) 52°C

Other dewatering aids

In addition to the products listed above, specific dewatering aids

have been developed for use in the dewatering of alumina trihydate

in the Bayer process. These products are described in more detail in

Section 9.

Mining Chemicals Handbook

200

8.7 Bibliography

1. Akers, R., Flocculation, Institute of Chemical Engineers,

London, 1975.

2. Chiang, S. H., and D. He, “Filtration and Dewatering: Theory

and Practice”, Fluid/Particle Separation Journal, Vol. 6, p. 64, 1993.

3. Halverson, F. and H. P. Panzer, “Flocculating Agents”, Kirk-

Othmer: Encyclopedia of Chemical Technology, Vol. 10, 3rd Edition,

pp. 489-523, John Wiley & Sons, Inc., 1980.

4. Heitner, H. I., “Flocculating Agents”, Kirk-Othmer: Encyclopedia

of Chemical Technology, Vol. 11, 4th Edition, pp. 61-80, John Wiley

& Sons, Inc., 1994.

5. Heitner, H. I., T. Foster, and H. P. Panzer, “Mining Applications,

Mineral Processing”, Encyclopedia of Polymer Science and

Engineering, Vol. 9, pp. 824-34, 1987.

6. Kitchener J.A., “Principles of Action of Polymeric Flocculants”,

British Polymer Journal, Vol. 4, p. 217, 1972.

7. Lewellyn, M.E., and P. V. Avotins, “Dewatering/Filtering Aids”,

Reagents in Mineral Technology, Surfactant Science Series, Vol. 27,

pp. 559-74, Marcel Dekker, Inc., 1988.

8. Linke, W. F., and R. B. Booth, “Physical Chemical Aspects of

Flocculation by Polymers”, Transactions American Institute Mining

Metallurgical Engineers, Vol. 217, p. 364, 1959.

9. Linke, W. F., and R. B. Booth, Reports on Progress in Applied

Chemistry, Vol. 60, p. 605, 1976.

10. Besra, L., Sengupta, D.K., and Roy, S.K., “Flocculant and

Surfactant Aided Dewatering of Fine Particle Suspensions: A

Review”, Mineral Processing and Extractive Metallurgy Review,

Vol. 18, pp. 67-103, 1998.

11. Farinato, R. S., Huang, S.-Y., and Hawkins, P., “Polyelectrolyte-

assisted Dewatering”, Colloid-Polymer Interactions, pp. 3-50, John

Wiley & Sons, Inc., 1999.

12. Hocking, M. B., Klimchuk, K.A., and Lowen, S., “Polymeric

Flocculants and Flocculation”, Journal of Macromolecular Science,

Reviews in Macromolecular Chemistry and Physics, Vol. C39,

pp. 177-203, 1999.

Flocculants and dewatering aids

201

13. Morey, B., “Dewatering”, Kirk-Othmer: Encyclopedia of Chemical

Technology, Vol. 8, 4th Edition, pp. 30-58, John Wiley & Sons,

Inc., 1993.

Mining Chemicals Handbook

202

BAYER PROCESS REAGENTS

Mining Chemicals Handbook

204

Section 9 Bayer process reagents

The Bayer Process, developed and patented by Karl Joseph Bayer in

1888, is used for the production of alumina from bauxite. The process

is based on the fact that hydrated aluminium oxides are soluble in

caustic at elevated temperatures and pressures. The solubility of

aluminium oxide varies widely according to the form in which it is

present. Alumina occurs in bauxite in the trihydrate form (gibbsite)

and as the monohydrate (boehmite and diaspore). The trihydrate is

more soluble than the monohydrate.

The process may briefly be described, as follows-

Bauxite is digested in caustic soda solution at elevated temperatures

and usually under pressure. After digestion, the solution containing

the dissolved aluminium oxide in the form of sodium aluminate has

suspended in it the residue from the bauxite. This insoluble residue,

called 'red mud,' consists predominantly of iron oxide, titania and

silica. The red mud is separated from the aluminium oxide rich

solution with the aid of synthetic flocculants in vessels referred to

as Thickeners, Decanters or Settlers. The terminology used is

dependent on the operating company. The clarified liquor is further

polished (mud particles removed) via filtration. Alumina trihydrate

is then precipitated from the liquor, filtered and washed before it is

calcined at extremely high temperatures. The product derived is

anhydrous Alumina, Al

The underflow (mud) from the Thickeners, in addition to the mud

removed at filtration, still has entrained in it a significant amount of

liquor containing caustic and alumina. Most of this is recovered by

washing the mud in a Counter Current Decantation Circuit (CCD

circuit). Synthetic flocculants are also used here to aid in the

mud/liquor separation process.

The entire process may be represented by the equations:

Extraction

.3H

O + 2NaOH = 2NaA1O

+ 4H

O (1)

Precipitation

2NaAlO

+ 4H

O = Al

.3H

O + 2NaOH (2)

Calcination

.3H

O = Al

+ 3H

O (3)

Bayer process reagents

205

Mining Chemicals Handbook

206

A simplified flowsheet of the Bayer Process is shown in Figure 9-1

below. The dissolution and mud separation stages are generally

referred to as the "Red Side" of the circuit while the precipitation,

alumina filtration, and calcination are referred to as the "White Side."

Figure 9-1

A wide variety of chemical reagents is used in the various stages of

the process and these are described below. Because of the unique

conditions (liquor temperatures, high electrolyte levels etc.) in the

process streams, specialized techniques are generally required for

testing and using the various reagents in both the laboratory and

plant. Also, optimum reagent dosages vary widely owing to the

widely-varying nature of different bauxites and the red muds they

produce. We recommend that you consult your Cytec representative

for detailed information before testing our products.

9.1 Red mud flocculants

Up to the mid-1970s, starch was the most common flocculant used

in the separation of red mud from the pregnant liquor. The intro-

duction of high molecular weight, synthetic polyacrylate flocculants

at that time provided several advantages compared to starch.

• Higher thickener and washer underflow densities.

• Higher vessel throughputs.

STOCKPILE

BLENDING

MILLING

/SLURRYING

SPENT

LIQUOR

BAUXITE

FROM MINES

RAW CAUSTIC

ADDITION

SLURRY

STORAGE

DIGESTION

BLOW-OFF

TANK

SAND

REMOVAL

FILTERS

THICKENERS

WASHER

TEST

TANK

SPENT

LIQUOR

TANK

TERTIARY

SETTLERS

SE CO NDA RY

SETTLERS

PRIMARY

SETTLERS

PRECIPITATION

HYDRATE

STORAGE

WASH

TANK

WASH

TANK

FILTERS

CALCINATION

PRODUCT

AL203

BAYER PROCESS FLOW SHEET

SAND DISPOSAL

RESIDUE

TO WASH

CIRCUIT

FINE SEED

COARSE SEED

CONDENSATE

MUD TO DISPOSAL

(VIA FILTERS)

WASH WATER

• Higher washing efficiency resulting in reduced alumina and soda

losses.

• Improved pumpability of the underflow muds.

• Elimination of rodent problems and bacterial growth.

• Much lower dosages, thereby reducing handling and storage costs.

Cytec is a major supplier of these flocculants in both dry-powder

and emulsion forms. These flocculants are available in a range of

anionic charges and the optimum flocculant for any particular stage

of the red mud circuit is dependent on the soda content of the

liquor. In the thickener stage, where the soda level is very high, the

more highly anionic flocculants are the most effective. As the soda

level decreases down the washer train, flocculants of lower anionic

charge can be used. Cytec pioneered and patented the use of medium

anionic copolymer flocculants in the washer stages. For logistical

reasons, the number of different flocculants used in the red mud

circuit is generally limited to two or three products.

9.1.1 Cytec’s standard dry red mud polyacrylate

flocculants

SSUUPPEERRFFLLOOCC AA--119900 AA--118855 AA--117700 AA--115500 ffllooccccuullaannttss

--------------> Decreasing anionicity

9.1.2 Cytec’s emulsion red mud polyacrylate

flocculants

SSUUPPEERRFFLLOOCC 11222277 11222299 11223300 11223322 11223366 11223388 11224400 ffllooccccuullaannttss

--------------> Decreasing anionicity

9.1.3 Cytec’s hydroxamated polyacrylamide red

9.1.3 mud flocculants

In the late 1980s, Cytec introduced a range of proprietary emulsion

products incorporating new chemistry based on hydroxamated

polyacrylamide (HXPAM). These unique flocculants have since

replaced polyacrylates in the thickener (and, in some cases, first

washer) stages in many alumina plants around the world. Copolymer

flocculants continue to be used in the washer train where overflow

clarity is not a major requirement.

Bayer process reagents

207

The advantages of Cytec’s HXPAM flocculants include:

• Greatly improved thickener overflow clarities resulting in higher

liquor filtration rates, easier cake release, and reduced costs. Even

in cases where suspended solids content is not significantly

reduced, the liquor is still easier to filter since the fine mud

particles therein are present as small flocs (pin flocs) rather than

as dispersed individual particles.

• Faster mud settling rates without sacrificing overflow clarities,

thereby increasing plant throughputs and/or reducing the

number of thickeners on-line.

• Some muds which can not be adequately settled using polyacrylate

flocculants can be handled using HXPAM flocculants.

• Higher thickener underflow densities, thereby reducing soda and

aluminate losses.

• Improved rheological properties of underflow muds, thereby

reducing the torque on thickener rakes, improving mud pumpa-

bility, and permitting higher underflow densities.

• Reduction in the amount of lime needed in digestion. This is due

to the high affinity of the hydroxamate group for the Fe ions

which are present on the red mud particles, rather than relying on

Ca ion activation which is needed for flocculation with polyacrylate

flocculants. The reduced lime consumption not only reduces costs

but can lead to higher quality alumina with reduced calcium content.

• One plant has found that the use of HXPAM in the red mud circuit

enabled the elimination of the need for crystal growth modifiers

in the alumina precipitation stage.

• It has generally been found that the use of HXPAM reduces the

amount of scaling in thickeners and related equipment. This

extends the thickener on-line time and reduces descaling costs.

Cytec's standard hydroxamated red mud flocculants are:

SSUUPPEERRFFLLOOCC HHXX--220000 HHXX--330000 HHXX--440000 ffllooccccuullaannttss

--------------> increasing degree of hydroxamation.

The optimum flocculant for any particular mud can be determined

only by experimentation.

Higher solids versions of HX-200, HX-300, and HX-400 are also

available as SUPERFLOC HX-2000, HX-3000, and HX-4000 flocculants

respectively. These products provide lower shipping and handling

Mining Chemicals Handbook

208