The consumption of cyanide during processing operations is a major economic cost in the extraction of gold from its ores, while the discharge of cyanide wastes may result in significant environmental pollution. Many factors influence the levels of consumption and discharge of cyanide, including ore mineralogy and lixiviant solution chemistry. This paper proposes a robust methodology to estimate leaching cyanide consumption due to oxidation and reactions with gold, chalcopyrite and pyrite minerals forming various cyanide complexes, cyanate, thiocyanate and hydroxide precipitates of copper and iron. The method involves concurrent modelling of both the oxidation and leaching kinetics of minerals and the chemical speciation of the lixiviant solutions. The model was calibrated by conducting cyanide leaching experiments on pyrite, chalcopyrite, pyrite + chalcopyrite, pyrite + chalcopyrite + gold and pyrite + chalcopyrite + gold + quartz systems and determining the total Cu, Fe, Au and CN⁻ concentrations in solution. We show that this model can successfully estimate the formation of cyanide complexes and, hence, the consumption of cyanide.

In this study, precipitated calcium carbonate (PCC) has been produced using a semi-continuous carbonation process within a Ca(OH)_2(s)–CO_2(g)–H₂O system inside a bench-scale reactor. In order to understand the effects of the temperature, solid percentage of milk of lime (MOL), CO₂ gas injection rate, and agitation rate on the conductivity, specific surface area, microporous surface area (and subsequently agglomeration), and reaction termination time, an experimental procedure was used based on central composite design (CCD). Conductivity and pH were applied as the parameters controlling the reaction termination time. Using the data obtained from multiple regression analysis, the effects of the parameters on the abovementioned responses were obtained. The results showed that the conductivity has a direct relationship with the morphology; therefore, the conductivity level was considered as a parameter to determine the morphology. Moreover, the microporous surface area of the PCC was considered to determine the agglomeration. In this study, ultra-pure PCC samples with high specific surface areas and controlled morphologies (scalenohedral, cluster scalenohedral, rhombohedral, vaterite or chain-like agglomerates) were produced without adding any crystal growth modifier (CGM). The obtained PCC showed dimensions of 20 nm to 2 μm, with specific surface areas of 5.99–26.69 m² g⁻¹, purity of 99.86%, and a controlled morphology.

In this study, the effect of various ions with different radius and charge such as aluminum, calcium, and iron on the selective ion flotation of neodymium using sodium dodecyl sulfate as a collector was investigated. Firstly, the optimum conditions of neodymium ion flotation were determined by evaluating the main factors on the process efficiency including collector dosage, air flowrate, and pH. The optimum conditions for ion flotation of neodymium are as following: collector dosage = 21 × 10⁻⁴ M, air flow rate = 100 mL/min, and pH = 3 with 85.4% and 26.5% recovery for neodymium and water, respectively. Then, the effect of other ions on the ion flotation of neodymium was evaluated.