GB2024793A - Metal recovery from bimetallic salt complexes - Google Patents

Abstract

Metals are recovered from waste materials which contain an organic component and a bimetallic salt complex component which comprises complexes having the formula MIMIIXn &cirf& Aromatic and/or the formula MIMIIXn &cirf& MIIOX . Aromatic, wherein MI is a Group I-B metal, MII is a Group III-A metal, X is a halogen atom, n is the sum of the valences of MI and MII and Aromatic is a monocyclic aromatic hydrocarbon or halogenated aromatic hydrocarbon having 6 to 12 carbon atoms, by hydrolyzing the waste material with water and either hydrochloric acid or sodium hydroxide to form a hydrolysis mixture which separates into an organic phase and an aqueous phase, and, after removing the organic phase, recovering the Group I-B metal and the Group III-A metal from the aqueous phase. This process can be used, for example, to recover copper and aluminium from waste materials which contain CuAlCl4 &cirf& toluene and/or CuAlCl4 &cirf& AlOCl &cirf& toluene.

Description

SPECIFICATION Metal recovery from bimetallic salt complexes description.

This invention relates to a process for the removal of metals from waste materials which comprise bimetallic salt complexes having the generic formula M1M11Xn ~ Aromatic and/or the generic formula M1M11Xn ~ M"OXM11OX ~ Aromatic,Aromatic, wherein M1 is a Group I-B metal, M11 is a Group Ill-A metal, X is a halogen atom, n is the sum of the valences of M, and M11 and Aromatic is a monocyclic aromatic hydrocarboh having 6 to 12 carbon atoms or a halogenated aromatic hydrocarbon having 6 to 12 carbon atoms. More particularly, it relates to a process for recovering copper and aluminium from such waste materials comprising cuprous aluminium tetrachloride complexes.

Bimetallic salt complexes having the generic formula: M1M1jXn ~ Aromatic are known to be useful in the separation from gas mixtures of such complexible ligands as olefins, acetylene, aromatics and carbon monoxide. For example, U.S. Patent Specification 3,651,159 discloses a process in which a liquid sorbent comprising a solution of cuprous aluminium tetrahalide in toluene is used to separate ethylene, propylene and other complexible ligands from a gas feedstream.

The complexed ligands are recovered by ligand exchange with toluene. The resulting solution of cuprous aluminium tetrahalide ~ toluene in toluene is recycled and used to separate additional quantities of the complexible ligands from the feedstream. U.S. Patent Specification 3,647,843 discloses a process in which a hydrocarbon pyrolysis gas stream is contacted with a cuprous aluminium tetrachloride solution in toluene to separate acetylene from the gas stream as a solution of the complex: HC = CH ~ CuAICI4 in toluene. Acetylene is stripped from this complex with toluene and the cuprous aluminium tetrach bride ~ toluene complex is recycled.

In such processes, where a liquid sorbent containing a bimetallic salt complex is recycled without purification and is used for long periods of time, there is a gradual increase in the amounts of reaction by-products and other impurities in the sorbent, until sufficient impurities are present to interfere with the efficient operation of the process. For example, when the liquid sorbent is contacted with a gas feedstream which contains an olefin having 2 to 4 carbon atoms, some of the olefin reacts with the aromatic hydrocarbon or halogenated aromatic hydrocarbon in the sorbent to form alkylated aromatic compounds and some undergoes polymerization to form olefin oligomers.Any water present in the gas stream reacts with the bimetallic salt complex to form the complex M1M11Xn ~ M"OX Aromatic, which has limited solubility in the liquid sorbent.

When it contains amounts of these and other contaminants which are sufficient to coat heat exchangers, clog lines and otherwise foul the equipment, the liquid sorbent must be purified, for example, by cooling to precipitate a sludge comprising the slightly-soluble bimetallic salt complexes and separating this sludge from it, or replaced by fresh liquid sorbent.

When a Group I-B metal halide is reacted with a Group Ill-A metal halide in the presence of an aromatic hydrocarbon solvent to form the liquid sorbent, a small amount of sludge is usually also formed, which contains a major amount of the bimetallic salt complex MlMIIXn ~ M"OX,M11OX, resulting from the presence of contaminants such as M11OX and water in the reactants. This sludge, which is only slightly soluble in the liquid sorbent, is removed before the sorbent is used to separate complexible ligands from gas feedstreams.

Because of their high metal contents, the spent liquid sorbent, sludge separated from liquid sorbent and sludge formed during preparation of the liquid sorbent cannot be discharged into sewers or waste ponds without causing serious pollution problems.

In addition, it is economically desirable to recover the metals, which are usually copper and aluminium, from these waste materials.

Several processes have been proposed for the separation of metals from sludge and from spent liquid sorbents which comprise the bimetallic salt complex M,M"Xn ~ Aromatic. U.S. Patent Specification 3,845,188 discloses a process in which the Group I-B metal in the spent liquid sorbent is recovered as its halide, by contacting the liquid sorbent with anhydrous ammonia and separating the metal halide which precipitates from the sorbent It has been proposed to burn the waste materials, but since these materials contain about 30% of metal salts, this process leaves a substantial metal ash which must be disposed of in a manner consistent with environmental conservation. These processes are generally uneconomical and impractical to carry out on an industrial scale and they may cause pollution problems.

This invention relates to an improved process for the removal of metals from waste materials which comprise a bimetallic salt complex component containing the complex MIMIIXn ~ Aromatic, the com plex M,M"Xn M11OX Aromatic or a mixture of these complexes, and an organic component containing an aromatic hydrocarbon, a halogenated aromatic hydrocarbon, an alkylated aromatic hydrocarbon, olefin oligomers, tars our a mixture thereof.

These waste materials may comprise spent liquid sorbent which has been used to remove complexible ligands from gas feedstreams, sludge separated from freshly-prepared liquid sorbent or sludge separated from spent liquid sorbent. This process, which is more efficient and more economical to operate than that disclosed in U.S. Patent Specification 3,845,188 and which avoids the pollution problems associated with the previously-proposed process, provides an environmentally-safe procedure for the disposal of the bimetallic salt complex-containing waste materials and also provides an efficient procedure for the removal of metals from these waste materials.

In accordance with the process of this invention, metal is recovered from waste material comprising the bimetallic salt complex by: (a) hydrolyzing the waste material under either acidic or alkaline conditions; (b) allowing the hydrolysis mixture to separate into an upper organic phase and a lower aqueous phase; (c) separating the organic phase from the aqueous phase; and (d) recovering the M, and M11 metals from the aqueous phase.

After separation of the phases in step (b), the organic phase may be distilled to separate aromatic hydrocarbons from it or it may be incinerated without causing pollution problems.

The spent liquid sorbents from which metals can be recovered by the process of this invention are solutions of bimetallic salt complexes in an aromatic hydrocarbon or a halogenated aromatic hydrocarbon which may contain alkylated aromatic hydrocarbons, alkylated halogenated aromatic hydrocarbons, olefin oligomers, other bimetallic salt complexes and/ortars. The bimetallic salt complexes in the liquid sorbents have the generic formula M,M"Xn ~ Aromatic and/orthe generic for mula M1M1iXn ~ M"OXM11OX ~ Aromatic.Aromatic. M1 is a Group I-B metal, that is, copper, silver or gold. Copper (I) is the preferred metal. M11 is a group Ill-A metal, that is, boron, aluminium, gallium, indium or thallium.

Boron and aluminium are the preferred metals, aluminium being particularly preferred. X is halogen, i.e., fluorine, chlorine, bromine or iodine; it is preferably chlorine or bromine. The sum of the valences of M, and M11 is represented byn. Aromatic is a monocyclic aromatic hydrocarbon or halogenated aromatic hydrocarbon having 6 to 12 carbon atoms, preferably 6 to 9 carbon atoms, such as benzene, toluene, ethylbenzene, xylene, mesitylene, chlorobenzene, bromobenzene, iodobenzene, dichlorobenzene, dibromobenzene, chlorotoluene, bromotoluene, iodotoluene, or chloroxylene. It is preferably benzene or toluene.Illustrative of these bimetallic salt complexes are the following: CuBF4 benzene, CuBCI4 benzene, AgBF4 mesitylene, ASBCI, ~ xvlene, AgAlCI4 ~ xylene, AgAlBr4 bromobenzene,CuGaCl4 ~ toluene, Culni4toluene,Culnl4 1,2- dichlorobenzene and CuTI14 ~ p - chlorotoluene. The bimetallic salt complex in the waste material is usu ally CuAlCl4 ~ benzene, CuAlCI4 ~ toluene or CuAIBr4 ~ benzene.The aromatic hydrocarbon of halogenated aromatic hydrocarbon in which the bimetallic salt complex is dissolved is usually and preferably the same as that used in the preparation of the bimetallic salt complex, but if desired it may be a different one. The total amount of aromatic hyd rocarbon or halogenated aromatic hydrocarbon in the liquid sorbent, that is, the amount in the bimetal lic salt complex plus the amount used as solvent, is at least 10 mole percent of the amount of the bimetallic salt M1M11Xn present. Preferably, the amount of aromatic hydrocarbon or halogenated aromatic hydrocarbon is 100 to 450 mole percent of the amount of bimetallic salt. The particularly preferred liquid sorbents contain 25% to 75% by weight of CUAICI, benzeneinbenzeneorCuAlCl4 toluene in toluene.

The waste materials from which the metals can be removed by this process generally comprise a major amount of the bimetallic salt complex M,M"Xn M110X ~ Aromatic, which is usually CUAICI, ~ AIOCI toluene, and a minor amount of an aromatic hydrocarbon, such as benzene ortoluene. They may also contain other bimetallic salt complexes, such as M,M11Xn ~ Aromatic, which is usually CuAICI4 toluene or CuAlCI4 ~ benzene, organic reaction by-products and tars.They are preferably either (1) a liquid sorbent comprising a solution of cuprous aluminium tetrachloride in benzene ortoluene which has been used in a processforthe removal of carbon monoxide, ethylene or other complexible ligands from a gas feedstream until it contains an amount of such impurities as alkylated aromatic compounds, olefin oligomers, tars, CUAICI, ~ AIOCI and other sorbent-insoluble bimetallic salt complexes such that it interferes with the efficient operation of the ligand separation process and necessitates replacement of the liquid sorbent in the system, (2) a sludge comprising bimetallic salt complexes formed by the reaction of cuprous aluminium tetrachloride with small amounts of water, hydrogen sulphide, amines or alcohols, present as contaminants in the gas feedstream and separated from the cold liquid sorbent, or (3) a sludge formed during the preparation of the liquid sorbent and comprising a major amount of CuAICI4 ~ AIOCI and minor amounts of CUAICI, and either benzene or toluene. If the waste material contains a high concentration of tars, alkylated aromatic hydrocarbons and/or olefin oligomers, it may be diluted with from one-half to twice its volume of an aromatic hydrocarbon to improve its handling and pumping characteristics before it is treated by the process of this invention. It is preferably diluted with an equal volume of toluene.

In one preferred embodiment of the process of this invention, the waste material is contacted with water and sufficient alkali metal hydroxide, usually sodium hydroxide, to form a hydrolysis mixture having a pH either in the range of 5 to 7, preferably 6 to 7, or higher than 11 and in which substantially all of the copper has been converted to copper oxide and all of the aluminium to aluminium hydroxide. When hydrolysis is complete, the hydrolysis mixture separates into an upper organic phase which contains a major amount of toluene or benzene and a lower aqueous phase comprising a slurry of copper oxide and aluminium hydroxide. After separation of the organic phase from it, the slurry may be safely discarded in a waste-disposal pond or pit. If it is desired to convert the copper to a compound which is less soluble than copper oxide, the slurry may be treated with sodium hydrosulphide before it is discarded.

Alternatively, the slurry or metal compounds which have been separated from it can be sentto a metal processor for salvage. The separated organic phase may be incinerated or it may be distilled to separate toluene and benzene from it.

In a preferred embodiment of the invention, the waste material from which metals are to be removed is contacted with water and sufficient sodium hydroxide to form a hydrolysis mixture having a pH of at least 11. After removal of the organic layer from the hydrolysis mixture, precipitated copper hydroxide is removed from the aqueous phase by filtration. The copper hydroxide recovered may be used as landfill or it may be converted to copper metal. The filtrate contains soluble sodium aluminate, which can be converted to aluminium hydroxide, which can be used as a flocculation agent in a settling pond.

In another preferred embodiment of the process of the invention, the waste material is contacted with water which contains sufficient hydrogen chloride to convert substantially all of the copper and aluminium in the bimetallic salt complexes to their water-soluble chlorides. In most cases, from 5 to 50 parts by volume of 2% to 20% aqueous hydrochloric acid are used per part by volume of the waste material. Particularly good results have been obtained when 4 to 10 parts by volume of 5% to 15% aqueous hydrochloric acid are used per part by volume of the waste material. In order to obtain complete conversion of the metals to their chlorides, the pH of the hydrolysis mixture should desirably be in the range of 1.8-2.3 and preferably it is 2.0.When hydrolysis is complete, the hydrolysis mixture separates into an upper organic phase, containing a major amount of benzene ortoluene, and a lower aqueous phase, containing copper and aluminium chlorides.

The organic phase, which is separated from the aqueous phase, for example, by decantation, may be distilled to recover the toluene or benzene or it may be incinerated.

A reducing agent is added to the acidic aqueous phase, namely a metal, e.g. aluminium, iron or magnesium, in an amount stoichiometrically equivalent to the amount of copper in the solution, which causes substantially all of the copper to precipitate from the solution. The preferred reducing agent is aluminium because of its low equivalent weight.

Only 9 pounds of aluminium are required to produce 63.5 pounds of copper, whereas 18 pounds of iron or 12 pounds of magnesium are required to accomplish the same result. In addition, aluminium is low in cost and its use does not introduce another metal into the reaction products resulting from the metal-recovery process.

The precipitated copper is recovered from the aqueous solution by decantation or filtration and, as it is quite pure, it can be sent to a copper processor for salvage.

The filtrate, which contains aluminium chloride and hydrochloric acid, can be discarded without causing pollution problems. It is often preferred, however, for the aluminium in it to be recovered, by adding to it sufficient alkali metal hydroxide to bring it to a pH in the range from 5 to 7 to cause aluminium hydroxide to precipitate. Preferably, a 10% to 20% aqueous solution of sodium hydroxide is used to bring the filtrate to a pH in the range of 5 to 5.5.

When the free-flowing slurry produced in this way settles, a clear supernatant liquid, which is an aqueous solution of an alkali metal chloride, usually sodium chloride, can be separated from the precipitated aluminium hydroxide and discarded. The aluminium hydroxide recovered can be used, for example, as a flocculating agent in the treatment of water.

The invention is further illustrated by the following examples, in which all amounts are in parts by volume unless otherwise indicated.

Example 7 A. A liquid sorbent containing 28.6 mole percent of cuprous aluminium tetrachloride and 71.4 mole percent of toluene was prepared by adding 1.1 moles of cuprous chloride to 1 mole of anhydrous aluminium chloride in toluene. The resulting solution was filtered to remove unreacted cuprous chloride and insoluble impurities from it.

B. A gas mixture obtained by the pyrolysis of natural gas had the following composition: Hydrogen 560 mm.

Carbon monoxide 280 mm.

Acetylene 75 mm.

Methane 60 mm.

Carbon dioxide 25 mm.

The pyrolysis gas was fed at ambient temperature and 19 psia pressure to an absorption column in which it was contacted with an amount of the liquid sorbent of Example 1A which contained at least sufficient cuprous aluminium tetrachloride to react with all of the acetylene and carbon monoxide in the feed gas. The acetylene and carbon monoxide in the gas mixture reacted with the liquid sorbent as it travelled through the column, forming a solution containing the acetylene-cuprous aluminium tetrachloride complex and the carbon monoxide-cuprous aluminium tetrachloride complex. This solution was fed to a stripping column in which it was brought into contact with benzene vapour at 80 C. The mixture of benzene vapour and carbon monoxide leaving the column was cooled to 25 C. to separate the carbon monoxide from the benzene.The sorbent solution, which then contained cuprous aluminium tetrachloride and the acetylene-cuprous aluminium tetrachloride complex, was fed to a stripping column in which it was brought into contact with benzene vapour at 95 C. The vapour leaving the column was cooled to condense the benzene and separate it from the acetylene. The stripped sorbent was returned to the absorption column, where it reacted with additional amounts of carbon monoxide and acetylene in the gas stream.

C. After it had been used for several months in the process described in Example 1 B, the liquid sorbent contained impurities which interfered with its use in the removal of carbon monoxide and acetylene from the gas feedstreams and it was replaced with fresh liquid sorbent.

D. The spent liquid sorbent, which had a specific gravity of 1.22 was added incrementally to 240 grams of 15% aqueous sodium hydroxide solution.

During the addition, the hydrolysis mixture was stirred efficiently and its pH was monitored. When 100 ml of spent liquid sorbent had been added to it over a period of 15 minutes, the hydrolysis mixture, having a pH of 9.6 and a temperature which had risen to 800C, developed an upper phase consisting largely of toluene and a lower aqueous phase con taining about 75 ml of precipitated copper oxide.

When 110 ml of spent liquid sorbent had been added, the aqueous phase, which had a pH of 6.8, was a slurry having a paint-like consistency. Following the separation of the organic phase from it, the slurry was discharged to a waste-disposal pond. The organic phase was distilled and the recovered toluene was recycled to Step 1A.

Example 2 24 pounds of 50% aqueous sodium hydroxide solution and then 214 pounds of water were added to 127 pounds of a sludge comprising CUAICL ~ AIOCI, CUAICI, ~ toluene, toluene, alkylated toluenes and tars, while the hydrolysis mixture was being stirred.

The hydrolysis mixture, which had a pH of 6, separated into an upper organic phase and a lower aqueous phase comprising a slurry of paint-like consistency containing copper oxides and aluminium hydroxide. The organic phase was separated and distilled to recovertoluenefrom it.

42 pounds of 20% aqueous sodium hydrosulphide solution was added to the slurry to convert the copper oxides to copper sulphide. The resulting black slurry was pumped to a waste-disposal pond.

Example 3 A. A liquid sorbent prepared by the process described in Example 1A was used in the process described in Example 1 B to remove carbon monoxidefrom a gas stream. After it had been used in the process for several months, the liquid sorbent contained impurities which interfered with its use in the removal of carbon monoxide and acetylene from the gas feedstream and it was replaced with fresh liquid sorbent.

B. 25 parts of the spent liquid sorbent, which had a specific gravity of 1.22, were added to a mixture of 15 parts of concentrated hydrochloric acid and 150 parts of water at room temperature. The reaction mixture, which had a pH of 2, separated into an upper phase comprising 25 parts of toluene and a lower clear acidic aqueous phase. The phases were separated and the toluene phase was used to prepare fresh liquid sorbent.

2 parts by weight of powdered aluminium were added to the acidic aqueous phase. The copper which precipitated was collected and dried at 110 C.

4.5 parts by weight of copper were obtained.

The filtrate, which contained 4 ppm of copper, was diluted to 200 parts with water and then neutralized to pH 5 by the addition of 20 parts of 15% aqueous sodium hydroxide solution to produce a free-flowing slurry. After the slurry had settled for an hour, the clear supernatant liquid, which was an aqueous sodium chloride solution, was separated from the precipitated aluminium hydroxide.

Example 4 25 parts of a sludge comprising CuAlCI4 ~ AIOCI, CUAICI, ~ toluene, toluene, alkylated toluenes and tars was diluted with 25 parts of toluene. The resulting solution was added slowly to a mixture of 10 parts of concentrated hydrochloric acid and 100 parts of water. The reaction mixture separated immediately into two phases. The upper phase, which contained organic compounds, was separated and incinerated.

To the acidic aqueous phase was added 1 part by weight of powdered aluminium in two increments.

30 minutes after the aluminium had been added, the precipitated copper was separated from the aqueous solution. The filtrate contained 4 ppm of copper.

Sufficient 20% aqueous sodium hydroxide solution was added to the filtrate to bring its pH to 5.5.

The aluminium hydroxide which precipitated was allowed to settle and then collected. The clear supernatant liquid was discarded.

This process can be used in a similar way to recover metals from the other bimetallic salt complex-containing waste materials disclosed herein.

Claims (14)

1. A process for the recovery of metal from waste material which comprises a bimetallic salt complex component selected from complexes having the formula M,M"Xn ~ Aromatic, complexes having the formula M,M"Xn ~ M"OXM11OX ~ AromaticAromatic and mixtures thereof, wherein M, is a Group I-B metal, M11 is a Group Ill-A metal, X is a halogen atom, n is the sum of the valences of M, and M11 and Aromatic is a monocyclic aromatic hydrocarbon having 6 to 12 carbon atoms or a halogenated aromatic hydrocarbon having 6 to 12 carbon atoms, and an organic component selected from monocyclic aromatic hydrocarbons having 6to 12 carbon atoms, halogenated aromatic hydrocarbons having 6 to 12 carbon atoms, alkylated aromatic hydrocarbons, olefin oligomers, tars and mixtures thereof, which comprises: (a) hydrolyzing the waste material under either acidic or alkaline conditions; (b) allowing the hydrolysis mixture to separate into an upper organic phase and a lower aqueous phase; (c) separating the organic phase from the aqueous phase; and (d) recovering the M, and M11 metals from the aqueous phase.

2. A process according to claim 1, for the recovery of copper and aluminium, wherein the bimetallic salt complex component is selected from CuAlCI4 Aromatic, CuAlCI4 ~ AIOX ~ Aromatic and mix turesthereof, which comprises contacting the waste material in step (a) with water and either hydrochloric acid or sodium hydroxide, to form a hydrolysis mixture.

3. A process according to claim 2, which comprises contacting the waste material with water and sufficient sodium hydroxide for the hydrolysis mixture to have a pH above 5, the lower aqueous phase comprising a slurry of compounds selected from copper and aluminium oxides and hydroxides.

4. A process according to claim 3, wherein the aqueous phase separated in step (c) is contacted with sodium hydrosulphide to convert copper oxide in the slurry to copper sulphide.

5. A process according to claim 2, 3 or 4, wherein the hydrolysis mixture formed in step (a) has a pH in the range from 5 to 7.

6. A process according to claim 2,3 or 4, wherein the hydrolysis mixture formed in step (a) has a pH of at least 11.

7. A process according to claim 2, which comprises contacting the waste material with an amount of dilute hydrochloric acid sufficient for the hydrolysis mixture to have a pH in the range from 1.8 to 2.3.

8. A process according to claim 7, wherein the separated lower aqueous phase, which comprises an aqueous solution of cuprous chloride and aluminium trichloride is combined with aluminium in an amount stoichiometrically equivalent to the amount of cuprous chloride in the solution, the resultant precipitated copper is separated from the aqueous aluminium trichloride solution, sufficient 10%-20% aqueous sodium hydroxide solution is added to the aqueous aluminium trichloride solution to bring it to a pH in the range from 5 to 7 and thereby cause aluminium hydroxide to precipitate and the aluminium hydroxide precipitate is separated from the resultant aqueous sodium chloride solution.

9. A process according to claim 7 or 8, wherein in step (a) the waste material is contacted with 2 to 50 parts by volume of 2% to 20% aqueous hydrochloric acid per part by volume of the waste material.

10. A process according to any preceding claim, wherein the waste material is diluted with from one-half to twice its volume of an aromatic hydrocarbon before it is hydrolyzed.

11. A process according to any preceding claim, wherein the bimetallic salt complex component of the waste material is selected from CuAICI4 toluene, CuAlCI4 ~ benzene, CuAlCI4 ~ AIOCI toluene, CuAlCI4 ~ AIOCI ~ benzene and mixtures thereof.

12. A process according to claim 1, substantially as herein described.

13. A Group I-B metal when obtained by a process according to any preceding claim.

14. A Group Ill-A metal when obtained by a process according to any of claims 1 to 12.