Nickel removing by electrocoagulation of Ni(II)-NH3-CO2-SO2-H2O system. Kinetics, isothermal, mechanism and estimated cost of operation.

This study reports nickel removing by electrocoagulation of Ni(II)-NH3-CO2-SO2-H2O system at laboratory scale. Experiments were done using Al/Al pair electrodes at initial nickel concentration between 293 and 1356 mg·L-1 and under operation parameters of pH 8.6, current density 9.8 mA·cm-2, electrolysis time 30 min, and temperature 60 ºC. The obtained results show removal efficiencies between 97.7 and 99.7 %. Kinetics modeling suggested combined effects of external diffusion and nucleation, and as controlling step the chemical reaction and a possible autocatalytic contribution. The process followed the Langmuir´s isotherm with a maximum adsorption capacity of 7519 mg·g-1. ICP-OES, XRD and FTIR characterization of the precipitates indicated a typical Ni-Al layered double hydroxide structures with 33.4-40.7 % nickel and 6.3-7.0 % aluminum depending on initial nickel concentration. The operation costs of energy and electrode consumption were 320 - 537 $·t-1 of removed nickel.

Ammoniacal Carbonate Leaching: Effect of Dissolved Sulfur in the Distillation Operation.

The distillation process in the Ammoniacal Carbonate Leaching technology was studied at bench-scale and on industrial scale. The dissolved sulfur effect in the Product-liquor that feeds to the columns, on the Basic Nickel Carbonate (BNC) properties and the operation expenses was determined. When increasing the sulfur in the liquor, we augment the selectivity towards the sulfate formation in the BNC molecule; therefore the energy consumption to the BNC thermal decomposition in the calcination process increases. Also, the nickel dissolved in the columns effluent increases due to complex reaction with [SO4 2-] and [S2O3 2-] ions, thus the expenses for consumption precipitation reagent increase too. Feeding carbonated liquor in the range 1.60 ? NH3/CO2 < 1.80 and CO2-rich solution increases the CO2 in the BNC with decreasing in sulfate; then, the mean diameter particle increases, the filtration resistance and the cake moisture diminish, which augments the productivity and reduces the energy consumption in the process of filtration and calcination. Keeping a pH between 8.4 and 8.7 in the columns outlet the greatest economic benefit is obtained of 0,125 ($ · h-1) per (m3 · h-1) of Product-liquor.