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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 H 2 S(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 H 2 S(g) bubble diameter or increasing H 2 S(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. ga1 • A 3D CFD model of the gas-liquid sulfide precipitation reactor was developed. • The rate-limiting step is determined to be gas-liquid mass transfer process. • Adjusting H 2 S(g) parameters can realize the control of supersaturation distribution. • The experimental result agrees with the CFD simulations. • Our methodology provides a protocol for design and optimization of the reactor. [ABSTRACT FROM AUTHOR]