Extraction studies of aurocyanide using Macronet adsorbents: physico-chemical characterization

Ion exchange technology is situated during the last decade as an alternative to activated carbon in goldcyanide recovery process. The search for suitable resins to Au(CN)(2)(-) recovery from alkaline cyanide solutions has prompted the synthesis of new resins incorporating new functionalities or modifying the polymer network properties that solve many of the existing problems. A new type of ion-exchange resins (Macronet Hypersol MN100 and MN300) incorporating mixtures of tertiary and quaternary groups, linked onto a styrene-divinylbenzene macroporous hyper-reticulated network are evaluated in this work. The total N content is 0.85 mmol/g for MN-100 and 1.14 mmol/g for MN-300 and the proton exchange capacity is 0.45 mmol/g for MNIOO and 0.91 mmol/g for MN-300. Accurate titration curves were used to determine pK(a), values of the tertiary amine groups (pK(H(a)) = 6.2 +/- 0.2 and 6.9 +/- 0.2 for MN100 and MN300, respectively). The Hypersol Macronet resins (MN100 and MN300) extract Au(CN)(2)(-) via two different modes of metal extraction based on the tertiary amine groups of the resin and in the small portion of the quaternary ammonium groups present in the resins. The extraction isotherms of Au(CN)(2)(-) show loadings of 16 mg Au/g and >40 mg Au/g for MNIOO and MN300, respectively. Efficient stripping of Au(CN)(2)(-) from the resin was achieved by using ethanol/water or acetone/water solutions of sodium hydroxide and sodium cyanide. Metal extraction from cyanide solutions, including Brazilian mine leach solution, showed considerable preference for gold and silver in comparison to base metals (copper, iron and nickel). (C) 2004 Elsevier B.V. All rights reserved.