Identification of tin species released in solution during the water leaching of solids from the alkaline smelting (NaOH-KOH) of stanniferous ores

Abstract

Tin species were studied Makundju ores in DRCongo. Identification of tin species released in aqueous solution during leaching of solids from the alkaline smelting (NaOH-KOH) was done to prepare added-value mining products on tin ores mined in the eastern DR Congo. Prior to alkaline fusion to have the smelting products (SP), the initial sample (IS) was processed for tests and characterization of tin species. Alkaline fusion in molten KOH-NaOH system was used and leached solution was considered for further analyses. Various physicochemical techniques including X-ray fluorescence spectrometry (XRF), scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA) and FTIR spectroscopy were used to characterize the initial ore and the molten cake. Water leached cake solution at a solid/liquid ratio of 1:10 was used to identify and characterize tin species. ICP-OES analysis of the pH 11.9 solution revealed a content of 4506.3 ppm, which is equivalent to a 95.87% leaching yield. Such yield attests to the stable Sn(OH)^2-_6(aq) ion as confirmed by UV-Vis. Crystallizations of M₂Sn(OH)_6(s) (M = Na and/or K) was studied using XRD, FTIR and TGA. As pH decreases below 9, Sn(OH)^2-_6(aq) ion changes to other tin species such as Sn(OH)^-_5(aq), Sn(OH)_4(S), Sn(OH)⁺_3(aq), Sn(OH)²⁺_2(aq), Sn(OH)³⁺_(aq) and Sn(OH)⁴⁺_(aq). The stability of each the tin species was determined at different pH values in aqueous solution. Hence, alkaline hexahydroxostannate nanoparticles, used in many electronic applications, can be produced from tin ores.