Influence of selected parameters on scorodite crystallization process

M.Sc. Justyna Piwowońska, M.Sc. Zbigniew Szołomicki, Ph.D. Andrzej Chmielarz

Scorodite is characterized by very low solubility (Ksp = 10-21.7 ± 0.5) and high stability in a broad pH range. It is the most stable form of iron and arsenic combination thus is appropriate for storage as a final product of arsenic removal from material circuits in copper smelters. The influence of selected parameters i.e. temperature (40, 60, 80 and 95 °C), reaction time (1, 2, 4, 6, 7, 8 and 10 h), amount of seeds (0, 20, 40, 60, 80, 120 and 240 g/L), initial arsenic concentration (5, 10, 15, 20, 30, 35 and 40 g/L) as well as initial copper concentration (10, 15, 18, 20, 30, 40 and 50 g/L), on scorodite production at atmospheric pressure was examined. It was found that solid product containing scorodite with particle size of 15 – 35 μm and low arsenic leaching (equals 1.0 mg/kg) can be obtained using the following crystallization parameters: temperature > 95oC, Fe(III)/As(V) molar ratio in the range from 1 : 1 to 1.3 : 1, reaction time slightly longer than 6 h, seeds amount > 40 g/L, initial As(V) concentration from 5 to 15 g/L. It was recognized that copper concentration in the inlet solution has no effect on product quality. For all Cu(II) concentrations analyzed arsenic leaching was equal ~ 1.0 mg As/kg, defined by procedure described in the European Standard PN-EN-12457-4.