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Extraction of tin from oxidized soldering dross by carbothermic reduction and acid leaching

The melting of soldering scrap originating from the electronic industry produces inter alia oxide dross, composed mainly of SnO2, which is resistant to the lixiviants most commonly used for hydrometallurgical treatment. We have investigated the possibility of converting this SnO2 into a soluble form by carbothermic reduction using coke powder in the 800–1000 o C temperature range. The raw material for the experiments was obtained by increasing the SnO2 concentration in the dross skimmed from the tin bath by further oxidation at high temperature. The treated dross and the products were examined with scanning electron microscopy and X-ray powder diffraction (XRD). The efficiency of the treatment was determined by leaching the reduced material with boiling 6 mol dm –3 HCl solution. The obtained solutions were analyzed by atomic absorption to determine the dissolved portion of tin content. Under optimized conditions, it was possible to reach conversion rates higher than 90% of the originally insoluble tin-dioxide content.