Application of sodium- and biogenic sulfide to the precipitation of nickel in a continuous reactor

• Residual metal concentrations can reach values below 0.25 mg/L.
• Nickel removal is maximum at Ni/S ratios of 1.
• Particle size distributions were affected by agglomeration.
• Increased supersaturation affected both growth rate and agglomeration kernels.

Attention has been focused in recent decades upon the precipitation of metal sulfides from acid mine drainage (AMD) and pregnant leach solutions, due to the advantages of the sulfide precipitation process over traditional methods employing hydroxides. The aim of this work was thus to explore technologies for the precipitation of valuable metals, such as nickel using such sulfides (as either Na2S or biogenic sulfide). The recovery of nickel sulfide was improved when the initial pH of the solution containing each metal was set to 7. In such a condition the removal efficiency of nickel was 99.9%, corresponding to a residual level of 0.13 mg L−1 for nickel in solution. Kinetic parameters for precipitation were determined from the particle size distributions (produced in an MSMPR reactor) using the method of moments, where the growth and nucleation rates, as well the agglomeration kernel, were calculated. The precipitation of nickel at an initial pH of 7 showed a nucleation rate value of 8.16 × 1018# m−3 s−1, the highest volumetric growth rate (1.03 × 101 μm−3 s−1) and agglomeration kernel of 9.71 × 10−23m3 #−1 s−1. The biogenic sulfide was a suitable alternative to sodium sulfide for nickel removal. Both sodium sulfide and biogenic sulfide can be utilized to precipitate nickel as millerite (NiS), allowing the effluent compliant with environmental legislation.