WO2018068065A1

WO2018068065A1 - Ion exchange resins for the removal of cyanide

Info

Publication number: WO2018068065A1
Application number: PCT/ZA2016/050040
Authority: WO
Inventors: Martha Hendriette KOTZE; Stefan Fourie
Original assignee: Lanxess (Pty) Ltd.; Watercar Mining Ltd.
Priority date: 2016-10-07
Filing date: 2016-10-07
Publication date: 2018-04-12

Abstract

The present invention relates to the use of iron oxide / iron oxyhydroxide-containing anionic exchange resins for removing cyanides from water and aqueous solutions.

Description

Ion exchange resins for the removal of cyanide

The present invention relates to the use of iron oxide / iron oxyhydroxide-containing anionic exchange resins for removing cyanide from water and aqueous mediums.

Nearly 18% of total sodium cyanide production is used in mining around the world, mostly for gold recovery. Gold mining operations use very dilute solutions of sodium cyanide, typically in the range of 0.01% and 0.05% cyanide (100 to 500 parts per million). The sodium cyanide dissolves in water where, under mildly oxidizing conditions, it dissolves the gold contained in the ore. The resultant gold-bearing solution is called "pregnant solution." Either zinc metal or activated carbon is then added to the pregnant solution to recover the gold by removing it from the solution. The residual or "barren" solution contains a huge amount of toxic free cyanide or weak acid dissolvable cyanide (i.e. barren of gold) may be re-circulated to extract more gold or routed to a waste treatment facility even if this waste treatment cannot be easily performed. It exists several methods to remove cyanide or to detoxify cyanide-containing effluents include destruction by natural degradation, by biological processes, by chemical oxidants but it remains an ecological and an expensive treatment process to remove cyanide from mining waste water, in particular if this shall be purified to gain drink water.

One option to remove cyanide from aqueous solutions is the use of ion exchange resins and inorganic iron oxide/iron oxyhydroxide.

US 4,732,609 B describes a process for the recovering of cyanide by contacting the cyanide effluent with an anionic exchange resin and oxidizing the adsorbed cyanide by treating the anionic exchange resins with an oxidation agent. In a further step the hydrogen cyanide that is evolved can be recycled. Since the handling of this process is difficult specific security conditions have to be fulfilled which makes this process too expensive and technically unusable.

DD 236515 describes the use of strong acid cationic exchange resin in combination with a weak basic anionic exchange resin and a strong basic anionic exchange resin for the removal of cyanide from galvanic effluents whereby the strong basic anion exchange resin has been loaded with chromate. This process required the use of different kinds of ion exchange resin which cannot be easily technically applied and is, in addition, economically not advisable.

WO 97/14658 describes a process for purifying cyanide-effluent byadding to the effluent a microorganism culture and agitating the mixture in a chamber for 24-72 h followed by „

- 2 - feeding the mixture into a 2nd chamber and adding an anion-exchange resin of a specific gold affinity. Also this process is expensive, for instance due to employ expensive fermenter for the preparation of the microorganism, and often the appropriated microorganism are sensitive and the process is therefore, due to technical and economical reasons, not recommended.

The common ion exchange resins for the adsorption of cyanide known from the prior art still do not exhibit the desired properties, for instance, at least with regard to selectivity or capacity or cost reduction. There is therefore a need for ion exchanges and/or adsorbers which are specific for cyanide anions.

The solution to the problem and hence the subject-matter of the present invention is the use of iron oxide/iron oxyhydroxide-containing anionic exchange resins for the adsorption of cyanide from water and aqueous medium.

In a further preferred embodiment, the present invention relates to the use of iron oxide/iron oxyhydroxide-containing anionic exchange resins for adsorbing cyanides from water and aqueous medium which contain primary and/or secondary and/or tertiary amino and/or quaternary ammonium groups. In a further preferred embodiment, the present invention relates to the use of iron oxide/iron oxyhydroxide-containing weak-basic anionic exchange resins for adsorbing cyanides from water and aqueous medium which contains tertiary amino groups. Iron oxide/iron oxyhydroxide-containinganionic exchange resins prepared according to the phthalimide process will be preferred used according to the invention. In a further preferred embodiment, a macroporus, monodisperse, iron-oxide / iron oxyhydroxide weak- basic anionic exchange resins prepared according to the phthalimide process is used for the adsorption of cyanide from water and aqueous medium. Such kind of ion exchange resins are commercial available. In particular, LANXESS Deutschland GmbH delivers LEWATIT FO 36 which is an monodisperse, macroporus, iron oxide/iron oxyhydroxide-containing weak- basic anionic exchange resins prepared according to the phthalimid process and which contains tertiary amino groups and will be preferred used for the adsorption of cyanide from water and aqueous mediums according to the invention. The iron oxide/iron oxyhydroxide-containing anionice xchange resins can be prepared according to the chlormethylation process or according to the phthalimide process. As is generally known the chloromethylation process is one in which a chloromethylate is formed that is subsequently reacted with amines to form aminomethylated polymers. The iron oxide/iron oxyhydroxide-containing anionic exchange resins according to the invention will be preferred prepared according to the well-known phthalimide process. This process is helpful to reduce the crosslinking compares to the chloromethylation process and is helpful to prepare ion exchange resins with specific substitutions degrees. The phthalimide process comprises in general the following steps: a) converting monomer droplets composed of at least one monovinylaromatic compound and at least one polyvinylaromatic compound and also a porogen and at least one initiator, to crosslinked bead polymer and if necessary at least one monovinylically unsaturated acrylic compound, b) amidomethylating of this crosslinked bead polymer with phthalimide derivatives, c) converting the amidomethylated bead polymer to an weak-basic anion exchange resins having aminomethyl groups and / or (meth)acrylic acid groups and if need be d) allowing the weak-basic anion exchange resins to at least partly react by alkylation to give weak-basic or strong basic anion exchange resins with secondary and/or tertiary amino and/or quaternary ammonium groups.

Strong basic anionic exchange resins contain quaternary ammonium compounds. The alkylation step d.) is a well-known preparation step usually done, but not necessary required, by using chloroalkylating reagents, like for example, chloromethane.

The anionic ion exchange resins prepared according to step a.) to d.) can be loaded with iron oxide/iron oxyhydroxide groups as follows: a) bring the bead-form anion exchanger in aqueous medium in contact with iron(II) or iron(III) salts and b) the suspension obtained from a) has to be adjusted to pH values in the range of 2.5 to 12 by adding alkali metal or alkaline earth metal hydroxides, and the resulting iron oxide/iron oxyhydroxide-containing anionic ion exchange resins are isolated by known methods. Preferable, the iron oxide/iron oxyhydroxide-containing anionic exchange resins will be prepared according to the following steps: a) converting monomer droplets composed of at least one monovinylaromatic compound and at least one polyvinylaromatic compound and also a porogen and at least one initiator, to crosslinked bead polymer, b) amidomethylating of this crosslinked bead polymer with phthalimide derivatives, _t

- 4 - c) converting the amidomethylated bead polymer to an weak-basic anion exchange resins having aminomethyl groups and d) allowing the weak-basic anionic exchange resins to at least partly react by alkylation to give weak-basic or strong basic anion exchange resins with secondary and/or tertiary amino and/or quaternary ammonium groups and e) bring the bead-form anion exchange resins of step d.) in aqueous medium in contact with iron(II) or iron(III) salts and f) the suspension obtained from e) has to be adjusted to pH values in the range of 2.5 to 12 by adding alkali metal or alkaline earth metal hydroxides, and the resulting iron oxide/iron oxyhydroxide-containing anionic ion exchange resins are isolated by known methods.

For the preferred doping with iron, the anion ion exchange resins can be brought into contact with the iron salt solutions with stirring or by filtration in columns. Per mole of iron salt used, in this case, use is made of 1 to 10 mol, preferably 3 to 6 mol, of alkali metal hydroxide or alkaline earth metal hydroxide. Per mole of functional group in the ion exchanger, use is made of 0. 05 to 3 mol, preferably 0. 2 to 1.2 mol, of iron salt. The pH in the doping step is adjusted using alkali metal hydroxides or alkaline earth metal hydroxides, in particular potassium hydroxide, sodium hydroxide or calcium hydroxide, alkali metal carbonates or alkaline earth metal carbonates or hydrogen carbonates. The amount of iron in the iron oxide/iron oxyhydroxide-containing anionic ion exchange resins is in general between 5 % to 60 % by weight based on the weight of the iron oxide/iron oxyhydroxide- containing anionic ion exchange resins but could also achieve a higher or lower value. In a further preferred embodiment, the amount of iron in the iron oxide/iron oxyhydroxide- containing anionic ion exchange resins is between 15 % to 25 % by weight (delivery form) based on the weight of the iron oxide/iron oxyhydroxide-containing anionic ion exchange resins. In a further preferred embodiment, the amount of iron in the iron oxide/iron oxyhydroxide-containing weak-basic anionic ion exchange resins is between 15 % to 25 % by weight (delivery form) based on the weight of the iron oxide/iron oxyhydroxide- containing weak-basic anionic ion exchange resins. Iron oxide/iron oxyhydroxide-containing weak-basic or strong basic anion exchange resins are also well known ion exchange resins. US-AA 20080272055 describes a process for preparing an iron oxide/iron oxyhydroxide-containing weak-basic anionic exchange resins. EP-A 1568660 describes a process for preparing an iron oxide/iron oxyhydroxide-containing strong basic anion exchange resins. Iron oxide/iron oxyhydroxide-containing anionic exchange resins to be used as the basis in accordance with the invention for the adsorption of cyanide may be either heterodisperse or monodisperse. Preference is given in accordance with the invention to using monodisperse weak-basic anionic exchange resins. Their particle size is generally 250 to 1250 μιη, preferably 280 - 600 μιη.

In the present application, "monodisperse" refers to those substances in which at least 90% by volume or by mass of the particles have a diameter within the interval of ± 10% of the most common diameter.

For example, in the case of a substance having the most common diameter of 0.5 mm, at least 90% by volume or by mass is within a size interval between 0.45 mm and 0.55 mm; in the case of a substance having the most common diameter of 0.7 mm, at least 90% by volume or by mass is within a size interval between 0.77 mm and 0.63 mm.

The term "macroporous" is known to those skilled in the art. Details are described, for example, in J.R. Millar et al., J. Chem. Soc. 1963, 218. The macroporous iron oxide/iron oxyhydroxide-containing weak-basic anionic ion exchange resins have a pore volume, determined by mercury porosimetry, of 0.1 to 2.2 ml/g, preferably of 0.4 to 1.8 ml/g.

Cyanides containing water and aqueous mediums coming from mining waste water are often in the present of different kind of metals. Especially, during the gold recovery process several metals, as for instance gold, zinc, cadmium, copper, nickel and silver cations build cyanide complexes in the presence of cyanides. Complexes of cyanide and cadmium, copper, nickel, silver and zinc cations are called weak acid dissociable cyanides. The present invention is preferred applicable to remove weak acid dissociable cyanides.

The context of the invention encompasses all definitions of radicals, parameters and explanations cited above and below, mentioned in general terms or in preferred ranges, in any combination with one another, i.e. also between the respective ranges and preferred ranges.

A further embodiment of the invention is a process for purifying water and aqueous medium containing cyanides with iron oxide/iron oxyhydroxide-containing anionic exchange resins, characterized in that the water or aqueous medium will be brought in contact with an iron oxide/iron oxyhydroxide-containing anionic exchange resins. _r

- 6 -

If mining waste water containing cyanides shall be purified to gain drink water it is well known to start the process by employing a reverse osmosis unit. Unfortunately, often a cyanide leaking through the reverse osmosis membrane can be determined.

Therefore, a further embodiment of the invention is a process to remove cyanide from aqueous solutions or water whereby in a first step a.) the aqueous solution will be directed to a reverse osmosis unit and in the second step b.) the effluent feed water from the first step a.) will be contacted with an iron oxide/iron oxyhydroxide-containing weak-basic anionic exchange resins.

Cyanide can be easily eluated from the iron oxide/iron oxyhydroxide-containing anionic exchange resins via an exchange of, for example, by using OH^". The eluated cyanide can then be recycled preferred for recovery of gold.

According to the invention, preference is given to using NaOH or KOH for elution of cyanide iron oxide/iron oxyhydroxide-containing anionic exchange resins. However, it is also possible to use any other base which leads to the formation of FeOH groups, for example NH₄OH, Na₂C0₃, CaO, Mg(OH)₂, etc.. The elution of the cyanide from the iron oxide/iron oxyhydroxide-containing anionic exchange resins will be preferred performed by a pH value greater 11. But the elution could also be performed by lower pH values. At high concentrations of hydroxide, the iron can solubilise and iron will be lost.

One additional inventive embodiment of the invention is a process to remove cyanide from aqueous solutions or water whereby in a first step a.) the aqueous solution will be directed to a reverse osmosis unit and in the second step b.) the effluent feed water from the first step a.) will be contacted with an iron oxide/iron oxyhydroxide-containing anionic exchange resins and in the third step c.) the iron oxide/iron oxyhydroxide-containing anionic exchange resins from step b.) will be treated with an alkaline solution to eluate the cyanide. The iron oxide / iron oxyhydroxide anionic exchange resins adsorbs not only cyanide but also additionally uranium and arsenic.

The iron oxide/iron oxyhydroxide-containing anionic exchange resins can be used to purify waters and aqueous mediums of any type which contain cyanide, preferably drinking water, wastewater streams of the chemical and metallurgical industries or of refuse incineration plants, of pit waters or leachate waters of landfill sites and from mining waste water. The use of iron oxide/iron oxyhydroxide-containing anionic exchange resins for the removal of cyanide from mining waste water is preferred. The iron oxide / iron oxyhydroxide-containing anionic exchange resins, are preferably used in apparatus and plants suitable for their tasks.

These kinds of apparatus and plants can be flowed through by a liquid to be treated, preferably filtration units, more preferably adsorption vessels, especially filter adsorption vessels and columns, filled with the iron oxide/iron oxyhydroxide-containing anionic exchange resins for the removal of cyanides from water and aqueous mediums, preferably drinking water.

The present invention has several advantages. Among a high selectivity of the used iron oxide/iron oxyhydroxide-containing anionic exchange resins for the adsorption of CN^" , it is a cheap technology and removes traces of uranium and arsenic from waters or aqueous solutions as well.

Claims

Claims:

Use of iron oxide/iron oxyhydroxide-containing anionic exchange resins for adsorbing cyanide from water and aqueous medium.

Use according to Claim 1, characterized in that the iron oxide/iron oxyhydroxide- containing anionic exchange resins have been prepared by the phthalimide process.

Use according to Claim 1 or 2, characterized in that the iron oxide/iron oxyhydroxide-containing anionic exchange resins to be used are monodisperse.

Use according to one of Claims 1 to 3, characterized in that iron oxide/iron oxyhydroxide-containing anionic exchange resins are monodisperse and macroporous.

Use according to one of Claims 1 to 4, characterized in that the iron oxide/iron oxyhydroxide-containing anionic exchange resins is an iron oxide/iron oxyhydroxide-containing weak-basic anionic exchange resin.

Use according to one of Claims 1 to 5, characterized in that iron oxide/iron oxyhydroxide-containing weak-basic anionic exchange resins are monodisperse and macroporous and which contains tertiary amino groups.

Use according to one of Claims 1 to 6, characterized in that LEWATIT® FO 36 will be used as iron oxide/iron oxyhydroxide-containing weak-basic anionic exchange resins.

Use according to Claims 1 to 7, characterized in that the waters to be cleaned are wastewater streams of the chemical industry and of refuse incineration plants, of pit waters, leachate waters of landfill sites and from mining waste water.

Use according to Claims 1 to 8, characterized in that the iron oxide/iron oxyhydroxide-containing anionic exchange resins assembled in apparatus which can be flowed through by the liquid to be treated.

Use according to Claims 1 to 9, characterized in that weak acid dissociable cyanides were removed from water and aqueous medium.

11. Use according to claim 1, characterized in that the iron oxide/iron oxyhydroxide- containing anionic exchange resins is an iron oxide/iron oxyhydroxide-containing strong basic anion exchange resin which contain quaternary ammonium groups.

12. Process for purifying water and aqueous medium containing cyanides with iron oxide/iron oxyhydroxide-containing anionic exchange resins, characterized in that the water or aqueous medium will be brought in contact with an iron oxide/iron oxyhydroxide-containing anionic exchange resins.

13. Process for purifying water and aqueous medium containing cyanides with iron oxide/iron oxyhydroxide-containing anionic exchange resins according to claim 12, characterized in that in a first step a) the water or aqueous medium will be directed to a reverse osmosis unit and b) the effluent feed water from the step a.) will be brought in contact with an iron oxide/iron oxyhydroxide-containing anionic exchange resins.

14. Process for purifying water and aqueous medium containing cyanides with iron oxide/iron oxyhydroxide-containing anionic exchange resins according to claim 13, characterized in that in a third step c.) the iron oxide/iron oxyhydroxide-containing anionic exchange resins from step b.) will be treated with an alkaline solution to eluate the cyanide.

15. Process for purifying water and aqueous medium containing cyanides with iron oxide/iron oxyhydroxide-containing anionic exchange resins according to claim 14, characterized in that the alkaline solution has a pH value greater than 11.