Abstract
Silicate removal from scheelite flotation wastewater by flue gas desulphurisation waste (FGD gypsum) has been investigated. Systematic laboratory-scale experiments were conducted to evaluate silicate removal and formation mechanism of calcium silicate. Precipitation test results showed that silicate removal reached 90% at an initial silicon concentration of 2650 mg/L when the dose of FGD gypsum exceeded 20 g/L. Equilibrium speciation analysis showed that solution pH is the key factor affecting silicate removal. Silicate removal could be effectively improved to 95% when pH was reduced to 10. Kinetic analysis showed that reaction rate peaked in 60 s and attained equilibrium after 240 s. Scanning electronic microscopy coupled with energy dispersive spectroscopy (SEM-EDS) results confirmed the formation of calcium silicate and described its morphology features. The continuous pilot-scale test (100 mL/min) further demonstrated the feasibility of utilizing FGD gypsum for silicate removal. Similar results were observed in laboratory-scale experiments. Treatment cost totalled 0.18 $/m3.
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