Modified poly(styrene-co-maleic anhydride) resin for precious metal recovery

A modified poly(styrene-co-maleic anhydride) (PSMA)  resin utilized in an ion-exchange process to separate  gold chloride ions from acidic gold slurries is described  in the invention.

A method of making the polymer is disclosed, and the  polymer that has ability to be formed such that it  encapsulates magnetite to allow it to respond  positively to an applied magnetic force to retain the  loaded polymer out of solution. The polymer is a nano-  particle that has high selectivity and has been proven  through lab trials to have highest affinity for gold in  acidic PGM’s slurry.

Poly(styrene-co-maleic anhydride)(PSMA) is a commercially available  polymer, which can be found in various grades with maleic anhydride  contents between 6 and 50 % and molecular weights between 1000 and  300 000 g/mol. Modified PSMA nanoparticles with functional groups  exposed on its surface have been synthesized starting as copolymers of  styrene and maleic anhydride with maleic anhydride contents ranging from  20 – 35 wt%.

Surface functionalized poly(styrene-co-maleimide) (PSMI) nanoparticles  were synthesized by thermal imidization of the poly(styrene-co-maleic  anhydride). Stable water-based dispersions were obtained containing  spherical, mono-disperse PSMI nanoparticles with a narrow size  distribution and average diameters of 50 ± 5 nm. The specific surface area  of the bulk PSMI nanoparticles is 88.1 ± 2.2 m2/g with an average pore  diameter of 82 Å. Elemental analyses confirmed complete conversion of  PSMA into the PSMI derivative. The [AuCl4]- batch sorption extraction  occurred with extremely fast sorption kinetics with high dependence on

the agitation rate and achieved maximum gold loading capacity of 1.76  mmol/g (347.7 mg/g) based on Langmuir and Freundlich isotherm models  analysis.

Formation of superparamagnetic properties in the polymer  Alternative method revealed that the PSMI nanoparticle can also be  functionalized to have magnetic properties. Superparamagnetic magnetite  (Fe3O4) nanoparticles with a high degree of crystallinity and phase purity  were synthesized by a chemical co-precipitation of Fe2+ and Fe3+ salts. The  average diameters of the obtained Fe3O4 nanoparticles were about 7 – 8  nm. After PSMI nanoparticle synthesis in the presence of the Fe3O4  nanoparticles, TEM analysis confirmed that the magnetically responsive  PSMI nanoparticles consist of magnetite core – polymer shell structure.

Elution

The adsorbed gold chloride ions were recovered by treating with nitric  acid as an eluent with high recoveries that increased with the steady  increase in HNO3 concentration.

• Resin manufacturing

• Gold tailings treatment processing

• Treatment plants in mines

• e-Waste processing

• Precious metal refineries

• The high reactivity of the maleic anhydride  groups in the copolymer toward nucleophilic  reagents enables the manufacturing of new  materials with a variety of functionalities  depending on desired applications.
• The modified PSMA offers high selectivity  and an efficient process for extraction and  recovery of AuCl4 ions, especially in aqueous  solutions with low precious metal content.
•  The modified PSMA can be easily synthesized by a simple post-polymerization  reaction using inexpensive and readily  available raw materials.
• Synthesized by a simple post-polymerization  reaction using inexpensive and readily  available raw materials.
• The modified forms of PSMA, will allow it to  be used in gold extraction or other  applications.
• Modified PSMA in the form of nanoparticles  with a superparamagnetic core, allow  separation of the polymeric material from  solution (after gold adsorption) using a  magnetic field.

Prof Bert Klumperman, Department of Chemistry and Polymer Science , Faculty Science, StellenboschUniversity.

Prof Klaus R. Koch, Department of Chemistry and Polymer Science, Facultyof Science, StellenboschUniversity

Dr Eugene M. Lakay, Department of Chemistry and Polymer Science, Facultyof Science, StellenboschUniversity