Interactions between sulphide minerals and alkylxanthates 9. A vibration spectroscopic study of the interaction between arsenopyrite, millerite, molybdenite, orpiment and realgar and ethylxanthate and decylxanthate ions in aqueous solution

Abstract

The reactions between millerite, NiS, molybdenite, MoS 2, realgar, AsS, orpiment, As 2S 3, and arsenopyrite, FeAsS, and aqueous solutions of potassium ethylxanthate and decylxanthate have been studied. Qualitative analysis of the alkylxanthate species present on the mineral surfaces after treatment with aqueous solutions of potassium alkylxanthate has been made by means of diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Dialkyl dixanthogen is the sole alkylxanthate species present on millerite and molybdenite surfaces, and only small amounts are formed as detected by DRIFT spectroscopy. Arsenic(III) decylxanthate and didecyl dixanthogen are formed on the surfaces of the arsenic-containing minerals after treatment with an aqueous solution of potassium decylxanthate, while no ethylxanthate species were observed after the corresponding treatment with potassium ethylxanthate for solubility reasons. Large amounts of arsenic(III) decylxanthate and substantially smaller amounts of didecyl dixanthogen are formed on the orpiment surfaces. Small and about equal amounts of arsenic(III) decylxanthate and didecyl dixanthogen are formed on arsenopyrite and regular. These amounts are similar to those of didecyl dixanthogen on orpiment. The dialkyl dixanthogen is formed in a redox reaction between alkylxanthate ions and highly oxidising species on the surfaces of these minerals. This oxidising agent is most probably an oxidation product of the sulphur in the minerals, such as the S 2O 2− 8 and/or S 2O 2− 7 ions. These are probably formed in small amounts during the grinding of sulphide minerals in the presence of air when the shortest SS distance is less than 3.4 Å. The formation of arsenic(III) decylxanthate takes place through a dissolution—precipitation reaction where an arsenic(III) species is dissolved from the mineral surface and arsenic(III) decylxanthate precipitates back on the mineral surface in the presence of decylxanthate ions. The relationship between the alkylxanthate species formed on sulphide mineral surfaces during treatment with an aqueous solution of alkali alkylxanthate and the structure of the mineral is discussed for 16 different sulphide minerals.