Iron ore tailings valorization through separate characterization and upgradation of different tailings streams of an Iranian iron ore processing plant.

In iron ore processing plants, different tailing streams are usually transferred to the tailings thickener for partial dewatering and finally transferred to the tailings dam as a single stream. Therefore, the mixing of different tailings streams happens. This way can challenge the process of reprocessing the tailings in the tailings dam since the mixing of different tailings streams causes more complexity in the mineralogical composition as well as the chemical composition of the tailings in the tailings dam. To solve this problem, the idea of separate characterization and separate upgradation of different tailings streams of an iron ore processing plant was carried out and a comparison was made between the results of magnetic upgradation of each tailings streams with the total tailings (i.e., the tailings in the tailings dam, which is a mixture of different tailings streams of the plant). Hence, the different tailings streams of an iron ore processing plant were sampled and characterize for total iron, FeO content, particle size distribution, mineralogical composition by X-ray diffraction (XRD), magnetic behavior by Davis tube tests, and dry solid tonnage rate. The characterization results showed that the iron grade and dominant iron ore mineral vary from one stream to another tailings stream of the iron ore processing plant. For instance, the total iron content of different tailings streams varies in the range of 18.46 to 64.68% and the dominate iron ore mineral in the Cobber tailings was hematite, but in the other tailings streams it was magnetite. The magnetic upgradation of the Cobber and Rougher tailings and also the total tailings were performed separately by the wet magnetic separation at different magnetic field intensities of 2000, 3500, 5000, and 15,000 Gauss. A concentrate with the highest iron grade of 61.79% and yield of 52.15% was produced from magnetic upgradation of the Rougher tailings, but magnetic upgradation of the total tailings produced a concentrate with the iron grade of 37% and yield of 15.2%. A comparison between the magnetic upgradation of the total tailings and the Cobber and Rougher tailings revealed that the upgradation of Rougher tailings results in a concentrate with higher iron grade and yield than the total tailings.

Treatment of gold ore cyanidation wastewater by adsorption onto a Hydrotalcite-type anionic clay as a novel adsorbent.

The treatment of cyanide contaminated wastewater from a gold processing plant was performed by the synthesized nanostructured Layered Double Hydroxide (LDH) which has known as a Hydrotalcite-type anionic clay. LDH was synthesized by the co-precipitation process, characterized by X-ray fluorescence (XRF), X-ray powder diffraction (XRD), scanning electron microscope (SEM) Brunauer-Emmett-Teller (BET), Fourier-transform infrared spectroscopy (FTIR) and Wavelength Dispersive X-ray analysis (WDX) and applied for removal of free cyanide from both synthetic solution and mining effluent. The maximum particle size of synthesized LDH was determined to be 4 nm based on the Scherrer's equation. The maximum loading capacity of LDH, 60 mg/g, indicates that LDH is an interesting adsorbent for cyanide removal. The data modeling showed that the kinetic and equilibrium data best fitted by FPKM and RPIM, respectively, also, rate-controlling step in the adsorption process is intra-particle diffusion based on Weber-Morris plot, and the adsorption of CN- onto LDH is a two-step process. The thermodynamic studies confirm that the adsorption of free cyanide on Mg/Al LDH is a spontaneous and endothermic process. The energy of activation for adsorption of free cyanide on Mg/Al LDH was determined to be 6.14 kJ/mol, which is in the range physicochemical sorption. The mining wastewater treatment was performed by the synthesized LDH. The adsorption experiments showed that more than 90% of free cyanide was removed from the real solution during a short period of contact time, which confirms the ability of LDH for the treatment of industrial cyanide contaminated wastewater. Graphical abstract.

Process development for recovery of copper and precious metals from waste printed circuit boards with emphasize on palladium and gold leaching and precipitation.

A novel hydrometallurgical process was proposed for selective recovery of Cu, Ag, Au and Pd from waste printed circuit boards (PCBs). More than 99% of copper content was dissolved by using two consecutive sulfuric acid leaching steps in the presence of H2O2 as oxidizing agents. The solid residue of 2nd leaching step was treated by acidic thiourea in the presence of ferric iron as oxidizing agent and 85.76% Au and 71.36% Ag dissolution was achieved. The precipitation of Au and Ag from acidic thiourea leachate was investigated by using different amounts of sodium borohydride (SBH) as a reducing agent. The leaching of Pd and remained gold from the solid reside of 3rd leaching step was performed in NaClO-HCl-H2O2 leaching system and the effect of different parameters was investigated. The leaching of Pd and specially Au increased by increasing the NaClO concentration up to 10V% and any further increasing the NaClO concentration has a negligible effect. The leaching of Pd and Au increased by increasing the HCl concentration from 2.5 to 5M. The leaching of Pd and Au were endothermic and raising the temperature had a positive effect on leaching efficiency. The kinetics of Pd leaching was quite fast and after 30min complete leaching of Pd was achieved, while the leaching of Au need a longer contact time. The best conditions for leaching of Pd and Au in NaClO-HCl-H2O2 leaching system were determined to be 5M HCl, 1V% H2O2, 10V% NaClO at 336K for 3h with a solid/liquid ratio of 1/10. 100% of Pd and Au of what was in the chloride leachate were precipitated by using 2g/L SBH. Finally, a process flow sheet for the recovery of Cu, Ag, Au and Pd from PCB was proposed.

Equilibrium and kinetic studies on free cyanide adsorption from aqueous solution by activated carbon.

Adsorption equilibrium and kinetics of free cyanide onto activated carbon were investigated in the batch tests, and the effects of contact time (1-72 h) and initial cyanide concentrations in the range of 102-532 mg/L were studied. Linear regression was used to determine the best fit of equilibrium and kinetics expressions. The two-parameter models including Freundlich, Dubinin-Radushkevich, Temkin and four different linearized forms of Langmuir and three-parameter models including Redlich-Peterson and Koble-Corrigan were employed for fitting the equilibrium data and it was found that, three-parameter models fitted the data better than the two-parameter models and among the three-parameter models the equilibrium data are best represented by Koble-Corrigan model. A number of kinetic models including fractional power, zero order, first order, pseudo-first order, Elovich, second order, intraparticle diffusion and four different linearized forms of pseudo-second order models were tested to fit the kinetic data. The latter was found to be consistent with the data. Intraparticle diffusion plots show that the adsorption process of free cyanide is a two steps process. In the first step, the adsorption of cyanide is fast while in the second step, cyanide adsorption slows down.