The roasting of sulfide ores and concentrates is one of the most important steps in pyrometallurgical metal production from primary raw materials, due to the necessity of excess sulfur removal, present in the virgin material. Pentlandite is one of the main sources for nickel pyrometallurgical production. The knowledge of its reaction mechanism, products distribution during oxidation and reaction kinetics is important for optimizing the production process. Raw pentlandite-bearing ore from the Levack mine (Ontario, Canada) was subjected to oxidative roasting in the air atmosphere. A chemical analysis of the initial sample was conducted according to EDXRF (Energy-Dispersive X-Ray Fluorescence) and AAS (Atomic Adsorption Spectrometry) results. The characterization of the initial sample and oxidation products was conducted by an XRD (X-ray Diffraction) and SEM/EDS (Scanning Electron Microscopy with Energy Dispersive Spectrometry) analysis. Thermodynamic calculations, a phase analysis and construction of Kellogg diagrams for Ni-S-O and Fe-S-O systems at 298 K, 773 K, 923 K and 1073 K were used for proposing the theoretical reaction mechanism. A thermal analysis (TG/DTA—Thermogravimetric and Differential Thermal Analyses) was conducted in temperature range 298–1273 K, under a heating rate of 15° min−1. A kinetic analysis was conducted according to the non-isothermal method of Daniels and Borchardt, under a heating rate of 15° min−1. Calculated activation energies of 113 kJ mol−1, 146 kJ mol−1 and 356 kJ mol−1 for three oxidation stages imply that in every examined stage of the oxidation process, temperature is a dominant factor determining the reaction rate.

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The study on the biosorption of copper ions using raw eggshells as an adsorbent is presented in this paper. The influence of different process parameters, such as: initial pH value of the solution, initial Cu2+ ions concentration, initial mass of the adsorbent, and stirring rate, on the biosorption capacity was evaluated. The SEM-EDS analysis was performed before and after the biosorption process. SEM micrographs indicate a change in the morphology of the sample after the biosorption process. The obtained EDS spectra indicated that K, Ca, and Mg were possibly exchanged with Cu2+ ions during the biosorption process. The equilibrium analysis showed that the Langmuir isotherm model best describes the experimental data. Four kinetic models were used to analyze the experimental data, and the results revealed that the pseudo-first order kinetic model is the best fit for the analyzed data. Calculated thermodynamic data indicated that the biosorption process is spontaneous, and that copper ions are possibly bound to the surface of the eggshells by chemisorption. The biosorption process was optimized using Response Surface Methodology (RSM) based on the Box-Behnken Design (BBD), with the selected factors: adsorbent mass, initial metal ion concentration, and contact time.

Lead ions removal from aqueous solutions onto bean shells is presented in this paper. The experiments were conducted in a batch system. The bean shells samples were rinsed with distilled water before the adsorption experiments. The analysis of the rinsed water showed that a significant amount of alkali and alkaline-earth metal ions are transferred from the adsorbent structure into the rinsed solution during the rinsing process. The COD analysis showed that these waters should be treated before being discharged into the surrounding watercourses. The influence of different process parameters (the pH value of the solution, the initial metal ions concentration, and the initial mass of the adsorbent) on the adsorption capacity was investigated. The adsorption capacity was higher at higher pH values of the solution. The adsorption capacity showed a decrease with the increase in the mass of the adsorbent. The increase in the initial metal ions concentration was shown to lead to an increase in the adsorption capacity until 0.8 g dm-3, after which a slight decrease was noted. Characterization of the adsorbent was performed by SEM-EDX, DTA-TGA, and FTIR analysis. The SEM-EDX analysis indicates a change in the morphology of the sample after the adsorption, as well as that K and Mg are possibly exchanged with lead ions during the adsorption process. The results obtained by the DTA-TGA analysis showed a weight loss of 77.8 % in the temperature range from 20oC to 900oC. The FTIR analysis indicated that the amide group is involved in the adsorption process. The pseudo-second order kinetic model was shown to be the best fit for the analyzed data, which led to the conclusion that chemisorption was a possible way of binding lead ions onto the surface of the bean shells. The Hill isotherm model was the best model for the analyzed adsorption equilibrium data. Obtained thermodynamic data indicated that the adsorption process was spontaneous, endothermic, and disordered, in which lead ions are bound to the surface of the bean shells by chemisorption. The maximum achieved adsorption capacity was 46.36 mg g-1.