Nano zero-valent iron has been shown to be effective for the removal of nitrates from natural wastes and wastewaters. This work studies the application of surface-modified nano zero-valent iron as bimetallic Fe/Cu particles to remove high concentration of nitrates. Dispersed nano-Fe/Cu particles were synthesized by chemical reduction and examined by X-ray diffraction, scanning electron microscopy, and BET surface area analysis. Batch experiments were conducted to investigate the effectiveness of bimetallic particles on the reduction and removal of nitrates. The parameters investigated included the copper content (0.5, 5, 10, and 20% w/w) in zero-valent iron nanoparticles and the initial concentration of nitrates (100, 200, 300, and 500 mg/L). During the experiments, the aqueous solution was analyzed to determine the evolution of as well as , NH₃, and which were produced as intermediate and final products. Based on the results obtained, it was concluded that the optimum coating rate was 5% w/w copper in nano-Fe/Cu, resulting in more than 80% nitrate reduction in 20 min and complete removal within 1 h.

A hydrochloric acid hydrometallurgical process was evaluated for Ni and Co extraction from a low-grade saprolitic laterite. The main characteristics of the process were (i) the application of a counter-current mode of operation as the main leaching step (CCL), and (ii) the treatment of pregnant leach solution (PLS) with a series of simple precipitation steps. It was found that, during CCL, co-dissolution of Fe was maintained at very low levels, i.e., about 0.6%, which improved the effectiveness of the subsequent PLS purification step. The treatment of PLS involved an initial precipitation step for the removal of trivalent metals, Fe, Al, and Cr, using Mg(OH)₂. The process steps that followed aimed at separating Ni and Co from Mn and the alkaline earths Mg and Ca, by a combination of repetitive oxidative precipitation and dissolution steps. Magnesium and calcium remained in the aqueous phase, Mn was removed as a solid residue of Mn(III)–Mn(IV) oxides, while Ni and Co were recovered as a separate aqueous stream. It was found that the overall Ni and Co recoveries were 40% and 38%, respectively. About 45% of Ni and 37% of Co remained in the leach residue, while 15% Ni and 20% Co were lost in the Mn oxides.

Nano zero-valent iron (nZVI) is considered as a highly efficient reductant with wide applicability in the remediation of contaminated sites, due to the small particle size, large specific surface area, and high reactivity. In this study, nZVI was synthesized by mixing Camellia Sinensis extract (green tea, GT) with a ferric iron solution. Polyphenols in the GT extract act as: (a) strong reductants, reducing thus Fe(III) to its elemental state and (b) capping agents that stabilize the Fe(0) nanoparticles and inhibit their potential rapid oxidation. The remediation potential of ZVI nanoparticles, produced with the Green Tea method (GT-nZVI), for hexavalent chromium (Cr(VI)) was evaluated by column tests. The tests were carried out using polyethylene columns, with 2.63 cm internal diameter and ~10 cm length. The columns were filled with 65 g of natural soil and pure silica sand at a ratio of 50% w/w. The reductive capacity of GT-nZVI was examined for high (5 mg L⁻¹) concentration of hexavalent chromium in aqueous solution. The soil was initially treated in the first column by introducing 11 pore volumes of GT-nZVI suspension through the packed column while in the second column 24 pore volumes were introduced. It was found that about 210 and 420 mg of ZVI nanoparticles were retained by the soil during this stage in column I and in column II, respectively. After this step, the solution of hexavalent chromium was introduced in the columns at a flowrate of 1.2 mL min⁻¹, in order to determine the breakthrough curve of Cr(VI) in the immobilized GT-nZVI on the soil. The total amount of reduced Cr(VI) was equal to 17 mg in column I and 33 mg in column II. Based on the available experimental data, it was estimated that a GT-nZVI-treated zone in the subsurface, with a length (L) of 0.75 m, could provide a sufficiently long contact time in order to reduce Cr(VI) levels from 5 mg L⁻¹ to less than 5 μg L⁻¹, under the condition that groundwater Darcy velocity is either equal to or less than 0.1 cm min⁻¹.