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The production of fine particles from extremely high supersaturation has challenged the application of sulfide precipitation in treating heavy metal wastewater due to the difficulty of solid-liquid separation. To this end, a gas-liquid sulfide precipitation reactor for the removal of Cu2+ was designed by controlling the mass transfer and supersaturation levels during sulfidation processes. Particularly, a computational fluid dynamics (CFD) model of the reactor, integrating sulfidation reaction kinetics with two-phase flow hydrodynamics, was first built, followed by examining the effects of H2S(g) bubble diameter and flow rate. Based on the CFD simulation, the rate-limiting step of the gas-liquid sulfide precipitation reaction is the gas-liquid mass transfer process. Either reducing H2S(g) bubble diameter or increasing H2S(g) flow rate can result in the control of reaction rate and supersaturation level in the system. In order to validate the CFD simulations, we measured Cu2+ concentrations during the sulfidation process with the batch experiments. The agreement between computational and experimental results indicated that our mechanistic model can provide a protocol for the design and optimization of the reaction system, allowing one to visualize the time-dependent reaction process and evaluate the performance of a reactor.

A series of ex-situ precipitation experiments were firstly performed to investigate the effects of Eh/pH and impurity molar ratio on the transition of arsenic bearing precipitates from amorphous phase to crystalline phase. Based on the analyses of the ex-situ experiments, another series of in-situ precipitation experiments were designed and conducted to explore the effects of current density, circulation pattern, inlet position, seed crystals' concentration, and impurity molar ratio on the formation and growth of crystalline precipitates containing arsenic. It was found that higher Eh and pH values, as well as the impurity ratio of Sb/Bi