WO1989009192A1

WO1989009192A1 - Hydrometallurgical effluent treatment

Info

Publication number: WO1989009192A1
Application number: PCT/AU1989/000144
Authority: WO
Inventors: David Roger Dixon; Tiong Chee Ha
Original assignee: Commonwealth Scientific And Industrial Research Or
Priority date: 1988-03-31
Filing date: 1989-03-31
Publication date: 1989-10-05
Also published as: KR900700397A

Abstract

A method for removing metal ions from solution, which comprises contacting the solution with a particulate mineral or clay material, in the presence of an alkali or alkaline earth metal oxide, hydroxide, carbonate or sulphide and a polyelectrolyte, whereby the particulate material becomes coated with a precipitate of the oxide, hydroxide, carbonate or sulphide of the metal(s).

Description

HYDROMETA LURGICAL EFFLUENT TREATMENT

This invention relates to a method for the recovery and/or removal of metal ions from aqueous solutions, especially effluents from mining and ore treatment processes.

Hydrometallurgy has evolved as firstly an art and now a science dedicated to the production of metals from mineral ores using solution (usually aqueous) processes rather than the high temperature approach of pyrometallurgy. There are three fundamental aspects: dissolution or leaching by chemical or biological means to solubilize the metals; concentration and/or separation of unwanted components; and recovery of the desired metal.

Methods of solution purification include cementation, crystallization, and precipitation as hydroxides, sulphides or carbonates. More recently used processes include ion exchange, solvent extraction and membrane processes such as reverse osmosis. Most of the latter require a preliminary solid-liquid separation to remove suspended matter and if possible some of the unwanted metal species.

The most common precipitation technique used is hydroxide treatment because of its relative simplicity, low cost of precipitant (lime), and ease of automatic pH control. In small plants, simpler and less expensive batch systems are more feasible, but a continuous treatment system can be used when flow rates are larger. The metal hydroxide precipitates tend to be colloidal and amorphous in nature, causing the resultant sludge to be voluminous and difficult to de-water. The other limitation associated with hydroxide treatment is that the presence of complexing agents severely inhibits hydroxide formation and precipitation.

Sulphide precipitation is an effective alternative to the above, with attractive features such as precipitation at lower pH values, lower sensitivity to the interference from complexing agents, greater selectivity with the possibility of recovery of specific metals, and less gelatinous sludges. However there are several disadvantages, including the potential for H2S gas evolution, environmental concern for sulphide toxicity and the problems associated with sulphide contamination of the mine circuit waters, which need to be recycled and used elsewhere on the mining site. The use of sodium carbonate to precipitate metals is another alternative.

Despite nearly three hundred years of success in mineral processing, there is increasing pressure to improve the efficiency of hydrometallurgical treatment.

This arises from a need to treat more complex and lower grade ores such as tailings and also from the need to protect our environment. Further, many Australian mines are in dry regions where water is a precious commodity which must be conserved both in quantity and in quality. The effects of water recycling with its attendant contamination problems on the efficiency of the different hydrometallurgical processes must also be considered.

We have now found that the problems associated with collecting and handling precipitates of metal hydroxides and other compounds can be at least minimised by the addition to suspensions of such precipitates of a particulate mineral or clay material and a polyelectrolyte,

By appropriate adjustment of the process conditions, the hydroxides or other compounds flocculate and collect around the particles to create floes which are more readily separated from the suspension, e.g. by settling or filtration.

According to one aspect of the present invention, there is provided a method for removing metal ions from solution, especially effluents from mining and ore treatment processes, which comprises contacting the solution with a particulate mineral or clay material, in the presence of an alkali or alkaline earth metal oxide, hydroxide, carbonate or sulphide and a polyelectrolyte, whereby the particulate material becomes coated with a precipitate of the oxide, hydroxide, carbonate or sulphide of the metal(s) . The particulate material may be derived from a wide variety of minerals and clays provided the nature of the mineral or clay is such as to permit the ready attachment to its surface of the metal hydroxide, carbonate or sulphide precipitate which is formed by the action of the alkali metal or alkaline eart _.h metal reagent. In this respect oxides, sulphates, silicates and carbonates are particularly useful. Examples of suitable minerals include calcium sulphate, calcium carbonate, magnesium oxide, zinc oxide, barium sulphate, silica and siliceous materials such as sand and glass. Suitable clay materials include mica, china clay and pyrophillite. This list is not exhaustive, however, and many other minerals and clay materials are suitable for use in the method of the invention.

In a preferred embodiment of this invention, the particulate material is a magnetic or magnetisable material. For this purpose iron oxides such as gamma iron oxide or magnetite are particularly suitable. Ferrites, such as barium ferrite or spinel ferrite, can be used.

Chromite (Cr0₂) can also be used. All of these oxides may be of natural or synthetic origin.

For use in the method of the present invention, the particle size of the magnetic material is not critical, but most usefully will be in the range of from 1 to 100 microns, usually about 50 microns. The particles should not be so small as to present handling problems.

Particles which are too large may tend to fall through the floes.

The method of the invention may be used for the removal of a wide variety of unwanted metal ions from mining and ore treatment effluents or for the extraction of wanted metal values from such solutions.

The metals to be removed or recovered may be present in solution as free (or solvated) metal ions or may be in the form of complex ions, e.g. chloride or cyanide complexes.

The amount and type of alkali or alkaline earth reagent (i.e. oxide, hydroxide, carbonate or sulphide) needed to produce the required precipitate will depend on the nature and concentration of the metals to be recovered and/or removed from solution.

Suitable reagents are sodium hydroxide, carbonate or sulphide, lime, magnesium oxide or calcined dolomite. Mixtures of these reagents may also be used.

The volume of the floes produced may vary considerably with the choice of reagent, and thus the choice of reagent will be influenced by this consideration. A fourfold or greater variation in settled floe volume may result when different reagents are used.

The pH required for the precipitation of the metal by the hydroxide, sulphide or other reagent is usually in range 3-12 and will be determined principally by the known chemistry of the metal or metals in the solution to be treated. However, the exact pH at which precipitation occurs may vary from the theoretical value because of the influence of other factors, such as the presence of other metal ions and/or differing metal ion concentrations, or the presence of complexing agents. Tests should always be carried out, therefore, to determine the optimum parameters. For example, precipitation of copper hydroxide can be effected at pH 7, when the concentration ^• of copper ions is about 2000 ppm. At 200 and 20 ppm, the pH required is 8 and 9, respectively.

The principal function of the polyelectrolyte is to trap traces of floes which do not become attached to the particulate material. The polyelectrolyte may be selected from a wide range of commercially-available materials. Laboratory tests with a range of commercial flocculants including those based on polyacrylamides and substituted polyacrylamides, polyamines and quaternary ammonium polyelectrolytes indicate that the main prerequisite for satisfactory performance is molecular weight; in general, the higher the molecular weight, the better the performance. The "Magnafloc" LT series of flocculants from Allied Colloids, which are based on poly(acrylamide) are of appropriate molecular weight (about 10^) and experiments with various types of polymers of about the same molecular weight but different charge shows a slight advantage for anionic flocculants such as LT 25.

The amount of polyelectrolyte required will generally depend on the nature and concentration of the metal(s) present in solution, and should not be such as to affect sludge density or interfere in the regeneration process. Amounts of 1 to 2 ppm have been found to be satisfactory, but larger or smaller amounts may also be used, again as determined by preliminary experiment.

The method of the invention can be perfomed using any suitable known apparatus. Stirring must be maintained to ensure that the particulate material is suspended in contact with the floes for a sufficient time to allow the attachment. Vigorous stirring should generally be avoided because it may tear the floes.

Separation of the loaded particulate material from the treated solution can be effected by any suitable known method, such as sedimentation or filtration. When magnetic materials are used, separation by magnetic means, e.g. in a magnetic separator, is particularly effective.

Regeneration of the particulate material is achieved by treating the loaded material with an acidic solution. By appropriate selection of the acid concentration, a low volume effluent can be produced which contains a high concentration of the metallic components. If the recovered metal is the valuable material then acid treatment will not only regenerate the added particulate material prior to recycle, but also provide a subsequent metal recovery stage, for example, electrowinning and cementation. If the precipitated material is waste then it can quickly be separated from the clarified product water and treated for metal recovery in a subsequent stage, if desired.

The following examples further illustrate the principles and practice of the invention. It will be understood, however, that the invention is not limited by these examples. 1 Example 1

3 One litre of a simulated cooling tower and filter cloth effluent, containing 50 mg/1 Zn, 560 mg/1 Ca and 5 12500 mg/1 Na was contacted with 10 g of magnetite

(1-10 μ) at pH 9.0 for fifteen minutes (pH was adjusted 7 with sodium hydroxide). The product water contained 0.9 mg/1 of Zn ions as determined by atomic absorption 9 spectroscopy. Acid regeneration of the loaded magnetite at pH 6.0 achieved a 100% recovery of Zn ions. 1

Example 2 3

In similar laboratory tests, 10 g of magnetite was 5 contacted with one litre of Yarra River water (Colour 45

Pt-Co units and Turbidity 14 NTU) , spiked with 50 mg/1 Cu 7 at pH 7.0 (pH was adjusted with sodium hydroxide). The product water was of colour, l Pt-Co unit and of 9 turbidity < 0.8 NTU and had a Cu concentration of 0.5 mg/1

1 Example 3

3 One litre of ore dump leachate containing 108 mg/1

Cu, 89 mg/1 Ca, 182 mg/1 Mg, 17.2 mg/1 Mn, 40.0 mg/1 Na, 5 9.4 mg/1 Al, 25 mg/1 Si and .,8 mg/1 Zn, was treated with

10 g of magnetite and 0.1 mg/1 of the nonionic 7 polyelectrolyte, LT 20 at pH 8.0 (pH was adjusted with sodium hydroxide). The product water contained 0.34 mg/1 9 of Cu. Acid regeneration of the loaded magnetite at pH

4.0 for 2.5 minutes achieved 100% recovery of the cupric 1 ions. i Example

3 One litre of a dump leachate containing 269.8 mg/1

Al, 777 mg/1 Ca, 80.9 mg/1 Cd, 538.7 mg/1 Cu, 73.6 mg/1 5 Fe, 1493 mg/1 Mg, 282.9 mg/1 Mn, and 10.88 g/1 Zn along with various amounts of trace elements was treated with 7 20 g of magnetite at pH 5.4 and 1.0 mg/1 of anionic polyelectrolyte LT 25 (pH was adjusted with a lime 9 slurry). The product water contained 7.45 mg/1 Al, 94.5 mg/1 Cu, 0.05 mg/1 Fe and 10.26 g/1 Zn. Whilst there has 11 been some loss of Zn and Cu, the primary objective was achieved, namely, the removal of Al and Fe. 13

Example 5 15

One litre of a highly concentrated leachate 17 containing 17.7 g/1 of Zn, 130 mg/1 Cu, 84.0 mg/1 Cd, 950 mg/1 Fe, 25.7 mg/1 Al, and 460 mg/1 Ca was contacted with 19 40 g of magnetite and 20 mg/1 of LT 25 at pH 6.0 (pH was adjusted with a lime slurry) to produce a clear water with 21 the following metal ion concentrations:

14.0 g/1 Zn, 0.17 mg/1 Cu, 71.6 mg/1 Cd, 560 mg/1 Fe, 0.8 3 mg/1 Al and 461 mg/1 Ca. To cope with the high level of chelated Fe in this leachate, in subsequent tests 20 ml of 5 20 volume hydrogen peroxide was added initially, which lowered the Fe level to 0.4 mg/1. The use of peroxide as 7 an oxidant to break the Fe-organic complex is an option available in those instances where almost total Fe removal 9 from a concentrated effluent is essential.

1 Example 6

3 One litre of dump leachate containing 24.3 mg/1 Al, 30.7 mg/1 Fe, and 543 mg/1 Zn at pH 3.77 was treated with 20 g of magnetite and 1.0 mg/1 LT 25 at pH 6.5. pH control was achieved using three different alkalies, caustic soda, a lime slurry and a saturated solution of sodium.carbonate. In each case greater than 99% of the Al was removed, but the results with sodium carbonate were vastly different for Fe and Zn: there being less removed than with the other alkalies. This raises the possibility of using different alkalies for treatment of different effluents.

Example 7

One litre of a leachate containing 6.2 mg/1 Al, 27.1 mg/1 Fe, 1.0 mg/1 Cu and 288 mg/1 Zn at pH 3.70 was treated with 20g of magnetite, 1.0 mg/1 LT 25 and 0.6g of sodium sulphide at pH 7.5. The alkali used in for pH control was a lime slurry. In this instance, the objective was the removal of virtually all metal ions to provide a clean water for use elsewhere in the mining circuit.

The water obtained contained < 20 mg/1 Zn and < 0.5 mg/1 Al, Fe and Cu.

Example 8

The experiment of Example 7 was repeated using a slurry of magnesium oxide for pH control.

The product water was of similar composition to that obtained in Example 7, but the settled volume of loaded magnetite floe was about half that observed when using lime for pH control. Example 9

One litre of a leachate containing 850 mg/1 Al,

125.9 mg/1 Fe, 83.7 mg/1 Cu, 13.9 mg/1 Cd, 0.17 mg/1 Cr, 9.62 mg/1 Ni, 85.5 mg/1 Mn and 22.60 mg/1 Zn at pH 2.50 was treated with 20 g of magnetite and 1 mg/1 LT 25 at the following pH values 7.95, 9.00, 10.42 and 11.60. The alkali used was caustic soda. The objective was the removal of all metals to below desired concentration levels, such as concentration levels specified by environmental authorities for discharge into natural water courses. Table 1 displays the composition of the water obtained at each pH.

TABLE 1

PH CONCENTRATION (mg/1)

Al Fe Cu Cd Cr Ni Mn Zn

7.95 0.11 0.16 0.02 3.44 0.03 0.14 39.0 6.38

9.00 0.09 0.18 0.01 0.23 OoOl 0.02 1.35 0.08

10.42 0.55 0.18 0.01 0.08 0.01 0.02 0.00 0.01

11.60 5.10 0.22 0.04 0.10 0.03 0.01 0.01 0.53

Claims

1. A method for removing metal ions from solution, characterised in that it comprises contacting the solution with a particulate mineral or clay material, in the presence of an alkali or alkaline earth metal oxide, hydroxide, carbonate or sulphide and a polyelectrolyte, whereby the particulate material becomes coated with a precipitate of the oxide, hydroxide, carbonate or sulphide of the metal(s) .

2. A method as claimed in Claim 1, characterised in that the particulate material is an oxide, sulphate, silicate or carbonate mineral or a clay.

3. A method as claimed in Claim 1 or Claim 2, characterised in that the particulate material is a magnetic or magnetisable material.

4. A method as claimed in Claim 3, characterised in that the particulate material is gamma iron oxide, magnetite or a ferrite.

5. A method as claimed in Claim 1 or Claim 2, characterised in that the particulate material is calcium, sulphate, calcium carbonate, magnesium oxide, zinc oxide, barium sulphate, silica, sand, glass, mica, china clay and pyrophillite.

6. A method as claimed in any one of Claims 1 to 5, characterised in that the particle size of the particulate material is from 1 to 100 microns.

7. A method as claimed in Claim 6, characterised in that the particle size of the particulate material is about 50 microns.

8. A method as claimed in any one of the preceding

Claims, characterised in that the metal ions to be removed from solution are in free, solvated or complexed form.

9. A method as claimed in any one of the preceding

Claims, characterised in that the metal ions to be removed from solution are in the form of chloride or cyanide complexes.

10. A method as claimed in any one of the preceding Claims, characterised in that the alkali or alkaline earth metal oxide, hydroxide, carbonate or sulphide is sodium hydroxide, carbonate or sulphide, lime, magnesium oxide, calcined dolomite or mixtures thereof.

11. A method as claimed in any one of the preceding Claims, characterised in that the polyelectrolyte has a molecular weight of about 10⁶.

12. A method as claimed in any one of the preceding Claims, characterised in that the polyelectrolyte is anionic.

13. A method as claimed in any one of the preceding Claims, characterised in that amount of polyelectrolyte added is 1 to 2 ppm.

14. A method as claimed in any one of the preceding Claims, characterised in that the amount of the alkali or alkaline earth metal oxide, hydroxide, carbonate or sulphide added to the solution is such that the pH of the solution is 3 to 12.

15. A method as claimed in any one of the preceding Claims, characterised in that the loaded particulate material is separated from the solution by sedimentation or filtration.

16. A method as claimed in any one of the preceding Claims, characterised in that the particulate material is a magnetic or magnetisable material and the loaded particulate material is separated from the treated solution by magnetic means.

17. A method as claimed in Claim 15 or Claim 16, characterised in that the particulate material is regenerated by treating the loaded particulate material with an acidic solution.