WO1997005292A1

WO1997005292A1 - Process for the removal of arsenic from bacterial leach liquors and slurries

Info

Publication number: WO1997005292A1
Application number: PCT/AU1996/000463
Authority: WO
Inventors: Michael Kenneth Rhodes; Peter Macrae; Aaron James King
Original assignee: Bactech (Australia) Ltd.
Priority date: 1995-07-25
Filing date: 1996-07-24
Publication date: 1997-02-13
Also published as: AUPN439395A0

Abstract

A process for the removal of arsenic from a bacterial leach liquor and slurry containing base metals which includes increasing the pH of the liquor or slurry from about 2.5 to about 4.5 by addition thereto of a base to precipitate arsenic material from the liquor or slurry.

Description

TTTLF,

"PROCESS FOR THE REMOVAL OF ARSENIC FROM BACTERIAL LEACH

LIQUORS AND SLURRIES"

DESC

The present invention relates to a process for the removal of arsenic from bacterial leach liquors and slurries.

FTF.I J) OF THE TNVFNTTON

Refractory sulphide material containing metals are traditionally roasted so as to decompose thermally the mineral sulphide matrix. Where the sulphide material contains arsenic, this results in the release of arsenic trioxide gas as well as sulphur dioxide gas. There is increased environmental pressure to reduce toxic gas emissions and this has resulted in mandatory installation of gas scrubbing systems in all roasting operations in Australia. The present invention will henceforth be described with reference to base metals particularly base metal sulphide concentrates.

The presence of significant levels of arsenic in base metal containing sulphide materials complicate the design and substantially increase the cost of gas scrubbing systems.

Bacterial oxidation of base metal containing sulphide materials results in a base metal rich liquor from which base metals may be recovered by solvent extraction and electrowinning. Where sulphide material contains arsenic then the liquor will also contain dissolved arsenic.

SUMMARY QF THE INVENTTON

The present invention provides a process for the treatment of arsenic containing bacterial leach liquors and slurries resulting from the bacterial oxidation of base metal containing sulphide materials in which the concentration of arsenic is reduced.

In accordance with one aspect of the present invention there is provided a process for the treatment of arsenic containing bacterial leach liquors and slurries resulting from the bacterial oxidation of base metal containing sulphide materials, wherein the bacterial leach liquor or slurry initially has a pH of about 2.0 or less, which comprises increasing the pH of the liquor or slurry to a level in the range from about 2.5 to about 4.5 so as to precipitate arsenic containing material from the liquor or slurry and separating the arsenic containing material precipitate from the liquor or slurry.

The liquor or slurry would also contain iron and in this case the arsenic is precipitated in the form of ferric arsenate which is an environmentally acceptable waste product.

Other base metals in the liquor or slurry may be copper, cobalt, nickel and zinc.

DESCRIPTION OF THF. INVENTION

Preferably, the pH of the liquor or slurry is initially about 1.3 and is increased to a value in the range from 2.9 to 3.5.

It has been found that in excess of 90% by weight of the arsenic present in the liquor or slurry can be removed by the process of the present invention.

The pH of the liquor or slurry may be increased by adding thereto a base such as ammonium hydroxide, calcium carbonate, lime or calcrete.

EXAMPLES

The present invention will now be illustrated by the following non limiting examples.

SlJBSTrrUTE SHEET (Rule 26) Example 1

Copper Concentrate

450mL of bacterial leach liquor obtained by bacterial leaching of a copper concentrate containing arsenic was agitated in a 500mL beaker.

The pH of the solution was measured and a sample taken to determine the quantity of the metals in the solution. The solution was then divided into three equal portions of 150mL.

The pH of each of the 150mL samples was raised using three different bases, lime, calcrete and ammonium hydroxide. The lime was a commercial grade containing calcium oxide, calcrete is a naturally occurring rock containing calcium carbonate. Ammonium hydroxide is a liquid.

For each solution sample the following procedure was adopted.

The solution was agitated and the pH measured continually. Small quantities of base were added until the pH of the solution reached approximately 2.0. A 400 microlitre sample of solution was removed. The pH was then increased by adding more base to pH 2.5 and a further 400microlitre aliquot removed. The pH was then raised to levels of approximately 3.0, 3.5, 4.0 and 4.5 using base and at each stage a 400 microlitre aliquot was removed.

Because small additions of the base affect the pH, the levels obtained were not exactly at 0.5 pH units. The actual pH levels are recorded in Tables 1.1, 1.2 and 1.3.

Each 400 microlitre aliquot was analysed for arsenic, iron and copper. The results are shown in Tables 1.1, 1.2 and 1.3. Copper Concentrate Solution Analysis At Different Stages of pH Adjustment Using Different

Neutralising Agents

Table 1.1 pH adjustment using - Lime

pH As Fe Cu ppm ppm ppm

1.41 1547 15345 9665

2.02 1541 15246 9635

2.52 1541 15114 9614

3.01 522 3892 8849

3.77 14 1918 7297

4.04 16 1875 3358

4.56 8 1276 3319

Table 1.2 pH adjustment using - Calcrete

pH As Fe Cu ppm ppm ppm

1.41 1586 15547 9604

2.00 1577 15466 9294

2.50 1551 15460 9294

3.00 612 6602 8737

3.64 16 2168 8737

4.00 5 2027 7899

4.50 5 1229 5242

4.71 5 55 3587 Table 13 pH adjusting using - Ammonium Hydroxide

pH As Fe Cu ppm ppm ppm

1.40 1547 16677 9522

2.08 1507 16224 9332

2.51 1484 16163 9207

3.00 1391 15148 8968

3.50 498 6091 8390

4.08 8 2076 7884

4.62 5 1849 6265

The extraction of the metals precipitated from the solution is shown in Tables 1.4, 1.5 and 1.6.

Copper Concentrate Extraction Levels (% by weight) Using Data From Tables 1.1, 1.2, 13

Table 1.4 pH adjustment using - Lime

pH As Fe Cu

% % %

1.41 0.0 0.0 0.0

2.02 0.4 0.6 0.3

2.52 0.4 1.5 0.5

3.01 66.3 74.6 8.4

3.77 99.1 87.5 24.5

4.04 99.0 87.8 65.3

4.56 99.5 91.7 65.7 Table 1.5 pH adjustment using - Calcrete

pH As Fe Cu % % %

1.40 0.0 0.0 0.0

2.00 0.6 0.5 3.2

2.50 2.2 0.6 3.2

3.00 61.4 57.5 9.0

3.64 99.0 86.1 9.0

4.00 99.7 87.0 17.8

4.50 99.7 92.1 45.4

4.71 99.7 99.6 62.7

Table 1.6 pH adjustment using - Ammonium Hydroxide

pH As Fe Cu

% % %

1.32 0.0 0.0 0.0

2.08 2.6 2.7 2.0

2.51 4.1 3.1 3.3

3.00 10.1 9.2 5.8

3.50 67.8 63.5 11.9

4.08 99.5 87.6 17.2

4.62 99.7 88.9 34.2

It will be seen from Tables 1.1 and 1.2 using lime and calcrete respectively as bases

SUBSTTTUTE SHEET (RULE 26) that as the pH was increased the amount of arsenic in solution decreased substantially where the pH was raised above pH2.5, further amounts being removed from solution as the pH value was increased. With the use of ammonium hydroxide as base as shown in Table 1.3 the amount of arsenic decreased substantially above pH3.0 and especially from pH3.5 upwards.

In fact with lime the amount of arsenic initially present in lime which removed by precipitation at about pH3.0 was about 66% by weight whereas with Calcrete the amount of arsenic initially present which was removed by precipitation at about pH3.0 was about 61 % by weight. With Ammonium hydroxide the amount of arsenic initially present which was removed by precipitation at about pH3.5 was about 68% by weight.

At about pH3.8 for lime the amount of arsenic precipitated had increased to above 99% by weight, whereas at about pH3.6 for Calcrete the amount of arsenic precipitated had also increased to about 99% by weight. With ammonium hydroxide at about pH4.1 the amount of arsenic precipitated had increased to about 99.5% by weight. With lime the amount of iron initially present which was removed by precipitation at about pH3.0 was about 75% by weight whereas with Calcrete at about pH3.0 the amount of iron precipitated was about 58% by weight of the amount initially present. With ammonium hydroxide the amount of iron initially present which was removed by precipitation at about pH3.5 was about 64% by weight.

At about pH3.8 for lime the amount of iron precipitated had increased to about 88% by weight, whereas at about pH3.6 for Calcrete the amount of iron precipitated had also increased to about 86% by weight. This was also similar with ammonium hydroxide at about pH4.1.

Thus, with lime and calcrete, 99% of the arsenic was removed at about pH3.6 - 3.8, whereas a higher pH of about 4.1 was required using ammonium hydroxide. In each case only minimal amounts of copper, nickel and cobalt were precipitated from the solution.

Example 2

Copper/Nickel Concentrate (1) 450mL of bacterial leach liquor obtained by bacteria' caching of a copper/nickel concentrate containing arsenic was agitated in a 500mL b . uker.

The pH of the solution was measured and a sample taken to determine the quantity of the metals in the solution. The solution was then divided inte ree equal portions of 150mL.

The pH of each of the 150mL samples was raised using three different bases, lime,

SUBSΗTUTE SHEET (Rule 26) calcrete and ammonium hydroxide. The lime was a commercial grade containing calcium oxide, calcrete is a naturally occurring rock containing calcium carbonate. Ammonium hydroxide is a liquid. For each solution sample the following procedure was adopted.

The solution was agitated and the pH measured continually. Small quantities of base were added until the pH of the solution reached approximately 2.0. A 400 microlitre sample of solution was removed. The pH was then increased by adding more base to pH 2.5 and a further 400microlitre aliquot removed. The pH was then raised to levels of 3.0, 3.5, 4.0 and 4.5 using base and at each stage an aliquot removed.

Because small additions of the base affect the pH, the levels obtained were not exactly at 0.5 pH units. The actual pH levels are recorded in Tables 2.1, 2.2 and 2.3.

Each 400 microlitre aliquot was analysed for arsenic, iron, copper, nickel and cobalt. The results are shown in Tables 2.1, 2.2 and 2.3.

Copper/Nickel Concentrate Solution Analysis At Different Stages of pH Adjustment Using Different

Neutralising Agents

Table 2.1 pH adjustment using - Lime

pH As Fe Cu Ni Co ppm ppm ppm ppm ppm

1.40 170 5384 9334 49 71

2.03 170 5364 9273 48 71

2.54 170 5349 9168 49 71

3.01 57 1774 9161 49 71

3.85 8 700 8660 49 71

4.03 10 648 8349 48 71

4.52 8 138 5097 46 66

Table 2.2 pH adjustment using - Calcrete

pH As Fe Cu Ni Co ppm ppm ppm ppm ppm

1.40 166 5320 9463 51 71

2.30 166 5320 9414 51 71

2.50 162 5312 9304 51 71

3.02 65 2264 9347 50 71

3.58 16 770 9140 50 71

4.01 8 642 8921 50 71

4.50 4 35 7414 50 71

Table 2 J pH adjustment using - Ammonium Hydroxide pH As Fe Cu Ni Co ppm ppm ppm ppm ppm

1.36 162 5579 9318 51 74

2.08 160 5545 9294 50 72

2.51 158 5529 9247 49 72

3.00 158 5504 9161 49 71

3.50 71 2113 8764 49 71

4.08 16 692 8584 49 71

4.62 10 402 7422 49 71

The extraction of the metals precipitated from the solution is shown in Tables 2.4, 2.5 and 2.6.

Copper/Nickel Concentrate Extraction Levels (% by weight) Using Data from Tables 2.1, 2.2, 23

Table 2.4

)H adjustment using - Lime pH As Fe Cu Ni Co

% % % % %

1.40 0.0 0.0 0.0 0.0 0.0

2.03 0.0 0.4 0.7 2.0 0.0

2.54 0.0 0.7 1.8 0.0 0.0

3.01 66.5 67.1 1.9 0.0 0.0

3.55 95.3 87.0 7.2 0.0 0.0

4.03 94.1 88.0 10.6 2.0 0.0

4.52 95.3 97.4 45.4 6.1 7.0 Table 2.5 pH adjustment using - Calcrete

pH As Fe Cu Ni Co

% % % % %

1.40 0.0 0.0 0.0 0.0 0.0

2.30 0.0 0.0 0.5 0.0 0.0

2.50 2.4 0.2 1.7 0.0 0.0

3.02 60.8 57.1 1.2 2.0 0.0

3.58 90.4 85.5 3.4 2.0 0.0

4.01 95.2 87.9 5.7 2.0 0.0

4.50 97.6 99.3 21.7 2.0 0.0

Table 2.6 pH adjustment using - Ammonium Hydroxide

pH As Fe Cu Ni Co

% % % % %

1.40 0.0 0.0 0.0 0.0 0.0

2.24 1.2 0.6 0.3 2.0 2.7

2.55 2.5 0.9 0.8 3.9 2.7

3.20 2.5 1.3 1.7 3.9 4.1

3.50 56.2 62.4 5.9 3.9 4.1

4.23 90.1 87.6 7.9 3.9 4.1

4.64 93.8 92.8 20.3 3.9 4.1

It will be seen from tables 2.1 and 2.2 using lime and calcrete respectively as bases as the pH was increased the amount of arsenic in solution decreased substantially above pH2.5 and especially from pH3.0 upwards. With the use of ammonium hydroxide as base as shown in Table 2.3 the amount of arsenic in solution decreased substantially above pH3.2 and especially from pH3.5 upwards. In fact with lime the amount of arsenic initially present which was removed by precipitation at about pH3.0 was about 66% by weight whereas with calcrete the amount of removal of arsenic at about pH3.0 was about 61% by weight.. With ammonium hydroxide the amount of arsenic removal at about pH3.5 was about 56% by weight. At about pH3.6 for lime the amount of arsenic removal was about 95% by weight. At about pH3.6 for calcrete the amount of arsenic removal was about 99% by weight. At about pH4.2 for ammonium hydroxide the amount of arsenic removed was about 90% by weight.

With lime the amount of iron initially present which was removed by precipitation at about pH3.0 was about 67% by weight. With calcrete at about pH3.0 the amount of iron removed was about 57% by weight whereas with ammonium hydroxide at about pH3.5 the amount of iron removed was about 62% by weight. At about pH3.6 the amount of iron removed had increased to about 87% by weight using lime, whereas at pH3.6 the amount of iron removed had increased to about 86% by weight using calcrete. With ammonium hydroxide the amount of iron removed had increased to about 88% by weight at about pH4.2. In each case only minimal amounts of copper, nickel and cobalt were precipitated between pH values of 2.5 and 4.2.

Thus, with lime, calcrete and ammonium hydroxide, 90-95% of the arsenic was removed from the solution as a precipitate with minimal losses of copper, nickel and cobalt from the solution.

Example 3

Copper/Nickel Concentrate (2)

500mL of bacterial leach liquor obtained by bacterial leaching of a copper concentrate containing arsenic was agitated in a 500mL beaker.

The pH of the solution was measured and a sample taken to determine the quantity of the metals in the solution. The solution was then divided into two equal portions of 250mL.

The pH of each of the 150mL samples was raised using three different bases, lime, calcrete and ammonium hydroxide. The lime was a commercial grade containing calcium oxide. The ammonium hydroxide was a liquid.

For each solution sample the following procedure was adopted.

The solution was agitated and the pH measured continually. Small quantities of base were added until the pH of the solution reached approximately 2.0. A 400 microlitre sample of solution was removed at intervals. The pH was then increased by adding more base to approximately pH 2.5 and a further 400microlitre aliquot removed. The pH was then raised to higher levels using base and at each stage an aliquot removed.

Because small additions of the base affect the pH, the levels obtained were not exactly at 0.5 pH units. The actual pH levels are recorded in Tables 3.1 and 3.2.

Each 400 microlitre aliquot was analysed for arsenic, iron and copper. The results are shown in Tables 3.1 and 3.2.

Neutralising Agents

Table 3.1 pH adjustment using - Lime pH As Fe Cu Ni Co ppm ppm ppm ppm ppm

1.28 6136 15744 734 1591 90

1.92 6075 16020 749 1669 94

2.86 415 4420 630 1637 100

3.97 26 1404 234 1234 76

4.70 20 1515 152 1138 70

5.13 20 796 47 949 59

Table 3.2 pH adjustment using - Ammonium Hydroxide pH As Fe Cu Ni Co ppm ppm ppm ppm ppm

1.32 5121 14456 720 1552 91

1.5 5090 14271 712 1550 92

1.73 5075 14228 712 1542 93

2.01 4909 14046 709 1532 93

2.61 2106 8477 697 1514 92

3.34 83 2432 666 1458 88

5.66 32 1493 266 1276 79

The extraction of the metals precipitated from the solution is shown in Tables 3.3 and 3.4.

Copper/Nickel Concentrate Extraction Levels (% by weight) Using Data From Tables 3.1, 3.2

Table 33 pH adjustment using - Lime pH As Fe Cu Ni Co

% % % % %

1.28 0 0 0 0 0

1.92 0.99 0 0 0 0

2.86 93.24 71.93 14.17 0 0

3.97 99.58 91.08 68.12 22.44 15.56

4.70 99.67 90.38 79.29 28.47 22.22

5.13 99.67 94.94 93.6 40.35 34.44

Table 3.4 pH adjustment using - Ammonium Hydroxide

pH As Fe Cu Ni Co

% % % % %

1.32 0 0 0 0 0

1.50 0.61 1.28 1.11 0 0.13

1.73 0.9 1.58 1.11 0 0.64

2.01 4.14 2.84 1.53 0 1.29

2.61 58.88 41.36 3.19 0 2.45

3.34 98.38 83.18 7.5 3.3 6.06

5.66 99.38 89.67 63.06 13.2 17.78

It can be seen from Tables 3.1 and 3.2 using lime and ammonium hydroxide respectively as bases that as the pH was increased the amounts of arsenic in solution decreased substantially above pH2.5 especially from about pH3.0 upwards.

In fact with lime the amount of arsenic initially present which was removed by precipitation at about pH2.9 was about 93% by weight whereas with ammonium hydroxi_'.f the amount of arsenic removed at about pH3.3 was about 98% by weight. At about r.H4 for lime the amount of arsenic removed was about 99.6% by weight.

With lime the amount of iron initially present which was removed by precipitation at about pH2.9 was about 72% by weight whereas with ammonium hydroxide the amount of iron removed at about pH3.3 was about 83% by weight.

With lime, the amounts of copper, nickel and cobalt precipitated at about pH2.9 were minimal. With ammonium hydroxide the amount of copper, nickel and cobalt precipitated at about pH3.3 were minor.

Thus, it can be seen that over 93% of the arsenic was extracted with lime, and ammonium hydroxide respectively, with minimal loss of the base metals in solution.

Example 4

Nickel Concentrate

In this series of tests a sample of solution was obtained by bacterial leaching of a nickel concentrate.

Lime and calcrete were added to separate 2000 mL samples of the solution which had an original pH of 1.3, to obtain a pH of between 2.3 and 2.5. The solution was kept agitated for six hours and additional base added to maintain the pH as required. After six hours the combination of precipitate and solution was filtered and the precipitate washed four times each with 1000 mL of water.

The results are shown in Table 4.1, for simplification the metal content solution has been equated to the original 2000 mL volume to offset the effect of th wash water.

Solution Analysis At Different Stages of pH Adjustment Using Different

Neutralising Agents

Table 4.1 pH adjustment using - Lime

pH As Fe Cu Ni Co ppm ppm ppm ppm ppm

1.3 885 27088 1593 16857 256

2.5 14 6096 1461 15832 241 pH adjustment using - Calcrete

pH As Fe Cu Ni Co ppm ppm ppm ppm ppm

1.3 838 25184 1573 16041 247

2.5 19 7121 1516 15589 240

Extraction Levels (% by weight) Using Data from Table 4.1

Table 4.2 pH adjustment using - Lime

pH As Fe Cu Ni Co

% % % % %

1.3 0 0 0 0 0

2.5 95.9 76.6 8.3 6.1 5.9

pH adjustment using - Calcrete

pH As Fe Cu Ni Co

% % % % %

1.3 0 0 0 0 0

2.5 94.3 71.7 3.6 2.8 2.7

From Tables 4.1 and 4.2 it can be seen that at pH2.5 the amount of arsenic removed by precipitation is between 94% and 96% by weight using lime and calcrete. Further, at pH2.5 the amount of iron removed was between 72% and 77% by weight in each case. Further, at pH2.5 only minimal amounts of copper, nickel and cobalt had been precipitated.

Example 5

Cobaltiferrous Concentrate

In this example, a pyrite concentrate containing cobalt was leached using bacterial leaching. The solution with a pH value of 1.33 was separated from the solids by filtration. 250mL of solution was retained and lime added until the pH reached 2.98. No intermediate samples were taken.

SUBSΗTUTE SHEET (Rule 26) The resulting precipitate was separated from the solution by filtration. The final solution which measured 260mL after washing, was analysed for arsenic, iron, cobalt and a number of other metals and elements.

Details of the solution analyses before and after lime addition of the specific metals are given in Table 5.1.

Solution Analysis

Table 5.1

PH As Fe Cu Ni Co ppm ppm ppm ppm ppm

1.33 100 34000 135 35 300

2.98 *0.6 *489 *125 *40 *296

* - Assays adjusted for volume of wash water. The extraction of metals from the solution is shown in Table 5.2.

Extraction Level (% by weight) Table 5-2

pH As Fe Cu Ni Co

% % % % %

1.33 0 0 0 0 0

2.98 99.4 98.6 7.6 0 1.2

In this example 99.4% by weight of the arsenic is extracted from the solution at about pH3.0, with minimal co-extraction of cobalt. Further, the amounts of iron removed by precipitation at about pH3.0 is 98.6% by weight.

In each of the examples, arsenic can be removed from the bacterial oxidation solution using lime, calcrete or ammonium hydroxide. Iron co-precipitates with the arsenic, whereas the metals of value such as copper, nickel and cobalt remain in solution to be recovered by conventional means. Arsenic Precipitate Stability

Precipitation of the solution arsenic in an environmentally stable form is a part of the process of the present invention. A solution produced from bacterial leaching of copper gold concentrate was assayed. pH As Fe Cu ppm ppm ppm

1.3 1069 8919 8330

Lime was added to this solution to increase the pH value to 5.0 then to pH7.0 and the solid precipitate separated from the residual solution by filtration. The stability of the arsenic in the solid precipitate was tested using United States Environmental Protection Agency multiple extraction method.

Multiple Extraction Procedure (MEP)

The multiple extraction procedure is designed to simulate the leaching that a waste will undergo from repetitive precipitation of acid rain on an improperly designed sanitary land fill. The repetitive extractions reveal the highest concentration that is likely to leach into the environment. The samples were extracted nine times using synthetic acid rain solution on a daily basis. If the concentration of the leached metals increases from the seventh or eight to the ninth day of extraction, the procedure is continued until the concentration decreases.

This test provides the most stringent conditions for establishing the long term stability of a solid waste and provides no opportunity for disguising the stability by adding an excess of base. The repetitive replacement of acidic solution at pH3.0 will consume any residual base and then dissolve any waste that was soluble under these conditions.

The arsenic released from solid precipitates in the stability testing was as follows.

Arsenic Release During Stability Testing

Day As ppm

1 0.3

2 0.1

3 0.2

4 n.d.

5 n.d.

6 n.d.

7 n.d

8 0.1

9 n.d In most countries the limit is 5 ppm of soluble arsenic, and all the results obtained were well below this limit. Modifications and variations such as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.

Claims

1. A process for the treatment of arsenic containing bacterial leach liquors and slurries resulting from the bacterial oxidation of base metal containing sulphide materials, characterised in that the base and leach liquor or slurry initially has a pH of about 2.0 or less, which includes increasing the pH of the liquor or slurry to a level in the range from about 2.5 to about 4.5 so as to precipitate arsenic containing material from the liquor or slurry and separating the arsenic containing material precipitate from the liquor or slurry.

A process according to claim 1, characterised in that the liquor or slurry also contains iron and that the arsenic is precipitated in the form of ferric arsenate.

3. A process according to claim 1 and 2, characterised in that the base material is copper, cobalt, nickel or zinc or a mixture thereof.

4. A process according to any one of the preceding claims, characterised in that the pH of the liquor or slurry is initially about 1.3.

5. A process according to any one of the preceding claims, characterised in that the pH is increased to a value in the range from 2.9 to 4.0.

6. A process according to claim 5, characterised in that the pH is increased to a value in the range from 2.9 to 3.5.

7. A process according to any one of the preceding claims, characterised in that the pH of the liquor or slurry is increased by addition thereto of a base.

8. A process according to claim 7, characterised in that the base is ammonium hydroxide, calcium carbonate, lime or calcrete.

9. A process according to claim 3, characterised in that minimal quantities of copper, cobalt and nickel are co-extracted thereby remaining in solution for further recovery processes.