Treatment of once rejected material – investigating the recovery of cassiterite from tailings disposals using different flotation methods

Tin-mining activities have taken place in the region of the German Erzgebirge (Ore Mountains) for over hundreds of years up until the late 1980s. For long times, gravity separation processes used to be the main beneficiation approach in those mining districts to recover cassiterite, the main tin-bearing mineral. Since for fine and very fine particles these approaches might not represent effective techniques, much valuable material could not be recovered and reported to tailings, where it was subsequently disposed. Thus, there are substantial amounts of cassiterite still present in these disposals, most of it as very fine particles with already high degrees of liberation. That fact brings these disposals into focus for potential reprocessing using beneficiation approaches, which are more sensitive to fine and very fine particles.

In this paper we present results concerning the laboratory-scale treatment of material from exemplary heaps of the former Altenberg and Ehrenfriedersdorf mining sites using various flotation methods. The material used is previously classified into different size ranges. Conventional froth flotation is applied to the fine particles (20µm – 100µm). For the very fine particle (< 20µm), special emphasis is put on oil-assisted flotation methods, including oil agglomeration flotation and two-liquid flotation. Therefore, an aliphatic oil phase of alkane basis is used to either selectively aggregate or collect the cassiterite particles. Recovery and flotation performance results are presented with respect to different process parameters: various collectors (e.g. sulphosuccinamates, phosphonic acids) and depressants (e.g. sodium fluorosilicate, oxalic acid) regime, oil dosage, oil/pulp agitation time and pulp density. Furthermore, the oil/particle aggregation behavior is analyzed via particle image analysis and, additionally, collector adsorption characteristics are investigated by contact angle measurements, zeta potential analysis and infrared spectroscopy. The data obtained is correlated with the testwork results achieved in order to interpret the flotation response of very fine cassiterite particles.