Optimized regimes of nepheline flotation using stockpiled apatite-nepheline processing waste (the Khibiny deposits)

Abstract

The task of processing stockpiled apatite-nepheline waste is of relevance and in line with the goal of ensuring environmental safety in Russia’s Arctic zone achievable through the reduction of accumulated environmental damage. The cost of processing secondary raw materials — when no grinding is required and thus most energy costs are saved — is much lower in comparison with the processing of natural raw materials. Around 1 billion tons of flotation waste have accumulated in the tailings ponds of Apatit-owned concentrator plants over the 90-year history of exploiting the Khibiny deposits. It poses a real threat of toxic pollution. In this regard, the development of beneficiation processes aimed at reducing waste that goes in the tailings ponds should be considered a priority area of research in the field of mineral processing. This paper describes the results of an extended laboratory study that looked at the concentratibility of two samples of apatite-nepheline flotation waste taken from two tailings ponds owned by Apatit which have different storage times. It is shown that the main valuable minerals in the tailings include nepheline (more than 50%), pyroxenes (5–7%) and titanite (about 4%). Three reagent regimes of reverse flotation were used to obtain nepheline concentrate: a basic regime that uses a mixture of coniferous and deciduous tall oil; a regime that uses alkyl hydroxamic acids to which distilled tall oil is added, and a regime that uses a mixture of tall oil and polyalkyl benzene sulfonic acids. The findings suggest that the regime that uses the mixture of alkyl hydroxamic and carboxylic acids with the addition of distilled tall oil provides the most efficient flotation regime that helps to selectively separate nepheline and darkcoloured minerals from the long-term storage tailings. The paper demonstrates feasibility of using apatite-nepheline processing waste (a case study of the Khibiny deposits) to produce nepheline concentrate, which serves as a material that can substitute imported non-bauxite raw materials required by aluminium industry.