Zhichang Liu a postdoctoral fellow at Illinois’ Northwestern University, and colleagues, have discovered of a new gold recovery process that’s based on a non-toxic component of corn starch. This could mean an end to the need to use cyanide in many gold recovery operations. More details will be published in the magazine’s July issue report on mineral processing advances. The paper Selective isolation of gold facilitated by second-sphere coordination with α-cyclodextrin has just been published – http://www.nature.com/ncomms/journal/v4/n5/full/ncomms2891.html

The abstract notes: “Gold recovery using environmentally benign chemistry is imperative from an environmental perspective. Here we report the spontaneous assembly of a one-dimensional supramolecular complex with an extended {[K(OH₂)₆][AuBr₄] (α-cyclodextrin)₂}_n chain superstructure formed during the rapid co-precipitation of α-cyclodextrin and KAuBr₄ in water. This phase change is selective for this gold salt, even in the presence of other square-planar palladium and platinum complexes. From single-crystal X-ray analyses of six inclusion complexes between α-, β- and γ-cyclodextrins with KAuBr₄ and KAuCl₄, we hypothesise that a perfect match in molecular recognition between α-cyclodextrin and [AuBr₄]⁻ leads to a near-axial orientation of the ion with respect to the α-cyclodextrin channel, which facilitates a highly specific second-sphere coordination involving [AuBr₄]⁻ and [K(OH₂)₆]⁺ and drives the co-precipitation of the 1:2 adduct. This discovery heralds a green host–guest procedure for gold recovery from gold-bearing raw materials making use of α-cyclodextrin—an inexpensive and environmentally benign carbohydrate.