Equilibrium and kinetic studies of ferricyanide adsorption from aqueous solution by activated red mud.

In this study, activated red mud (ARM) was used as a new adsorbent for the removal of ferricyanide anions from aqueous solution. Based on the percentage of ferricyanide removal and ferricyanide adsorption capacity, optimum conditions were evaluated using the response surface method (RSM) and central composite design (CCD). In optimum conditions (pH = 5.6, adsorbent dosage of 2.59 g, ferricyanide concentration of 60 ppm and contact time of 60 min), the percentage of ferricyanide removal and ferricyanide adsorption capacity were obtained as 79.6% and 1.8 mg/g, respectively. The kinetics and equilibrium studies were evaluated by considering the effective parameters including pH and ferricyanide concentration. Kinetic studies were evaluated by kinetic models of pseudo first-order, pseudo-second-order (four different linearized forms), Elovich and intraparticle diffusion. The results of the kinetic study indicated that the mechanism of ferricyanide adsorption onto the ARM adsorbent is a chemisorption interaction by a fast ferricyanide adsorption onto ARM and subsequently the slow diffusion of ferricyanide ions into the ARM inner adsorption sites. The equilibrium studies showed that the adsorption process followed the Langmuir model in which ferricyanide adsorption onto ARM was homogeneous with monolayer adsorption. The results indicated that the activation process of red mud improved adsorbent efficiency and increased the adsorption capacity.

Characterization studies of red mud modification processes as adsorbent for enhancing ferricyanide removal.

In this study, waste solids of the alumina industry (red mud) have been modified and utilized as a ferricyanide adsorbent which is characterized by XRD, XRF, FTIR, SEM, EDX, ICP and BET analysis. The four modification methods including the processes of washing with seawater (B), acid treatment Bauxsol (ATB), activated ATB using ammonia (ABA), and activated Bauxsol using cetyltrimethylammonium bromide (CTAB) (ABC) were evaluated to increase the reactivity of red mud (RM) for ferricyanide removal. The ferricyanide adsorption capacity was obtained at 12.40, 6.84, 2.95, 2.50 and 0.44 (mg/g) for ABC, ATB, ABA, B and RM, respectively. The CTAB with a concentration above the critical micelle concentration changed the negative charge of red mud to positive charge. It decreased the negative charge repulsion force between the Bauxsol surface and ferricyanide ions. The adsorption capacity of ferricyanide was decreased from 12.40 to 2.75 (mg/g) with increasing the adsorbent amount from 0.5 to 5 (g). The results showed that the activated Bauxsol using CTAB could be effectively used as a new adsorbent for ferricyanide ions from wastewaters.

Mathematical modeling on non-dispersive extraction of germanium from aqueous solutions using Aliquat 336.

In this work, the mathematical modeling of the facilitated transport of germanium (non-dispersive extraction) through a flat sheet membrane with an Aliquat 336 carrier was described. The flat sheet supported liquid membrane (FSSLM) experiments were performed under conditions germanium ≈ 100 mg/L, tartaric acid concentration of 2.76 mmol/L, and carrier concentrations of 2.5-10%v/v. The extraction equilibrium, mass transfer, and diffusion equations based on Fick's law were the principles of modeling. Modeling was carried out by programming in Matlab mathematical software to obtain the extraction (Kex) and mass transfer constants (Km) as the objective parameters. According to the model resolution, Kex and Km were found to be 0.178 and 9.25 × 10-2 cm/s, respectively. The correlation coefficients between model and experimental data relating to the Aliquat 336 concentrations of 2.5, 5, 7.5, and 10%v/v were found as 0.96, 0.98, 0.99, and 0.92. The parameters of root mean square error, bias, and scatter index showed the model accuracy. In addition, diffusion coefficients relating to Aliquat 336 concentrations of 2.5, 5, 7.5, and 10%v/v were calculated using mass transfer coefficients to be 2.4 × 10-4, 2.23 × 10-4, 1.91 × 10-4, and 1.79 × 10-4 cm2/s, respectively.

Recycling of hazardous waste as a new resource for nickel extraction.

Nickel extraction from hazardous waste by sulphuric acid leaching has been investigated. This study was performed to assess the effects of different parameters such as reaction time, acid concentrations, solid-liquid ratio, particle size, stirring speed and reaction temperature on nickel extraction from zinc plant residue, with the aim of recycling this waste and reducing its environmental impact. It was shown that the nickel extraction increased with increasing reaction time, acid concentration and temperature, and decreasing solid:liquid ratio and particle size. Leaching residues were subjected to chemical analysis, XRD and SEM studies, and the results indicated that it is possible to extract more than 96% nickel content by optimization of leaching conditions. These results provided important data on the recovery of nickel from toxic hazardous waste, and leaching is a suitable method for this waste management. The results also showed that this waste can be used as a secondary resource for nickel extraction.

Roadmap for recycling of germanium from various resources: reviews on recent developments and feasibility views.

Germanium as a strategic metalloid is widely used in high-tech devices. The most crucial germanium resources are rare and limited to zinc minerals, i.e., especially zinc sulfides and coal-related products. Other than coals and zinc minerals, materials such as WEEEs (wastes from electrical and electronic equipment) and catalysts are considered secondary resources of germanium. Since there is no specific mineral for germanium, it should be extracted from the resources above as a by-product. Primary resources contribute to 70% of germanium production, whereas the rest is produced from recycled materials. The world refinery production of germanium enhanced by about 7% in 2020 compared to 2019. This growing demand for germanium encourages the industry to find other resources and extraction technologies. Germanium can be recovered after leaching of different resources in acidic, water, or alkaline media followed by processing using various hydro/pyrometallurgical methods. Several reviews and articles have been published to review the resources and processes for the germanium separation. However, no one did not present a final road map from feasibility views and environmental aspects. This review proposes a road map for germanium recycling based on the performance and economic availability, process efficiency, operational issues, and process feasibility.

A review of zinc oxide mineral beneficiation using flotation method.

In recent years, extraction of zinc from low-grade mining tailings of oxidized zinc has been a matter of discussion. This is a material which can be processed by flotation and acid-leaching methods. Owing to the similarities in the physicochemical and surface chemistry of the constituent minerals, separation of zinc oxide minerals from their gangues by flotation is an extremely complex process. It appears that selective leaching is a promising method for the beneficiation of this type of ore. However, with the high consumption of leaching acid, the treatment of low-grade oxidized zinc ores by hydrometallurgical methods is expensive and complex. Hence, it is best to pre-concentrate low-grade oxidized zinc by flotation and then to employ hydrometallurgical methods. This paper presents a critical review on the zinc oxide mineral flotation technique. In this paper, the various flotation methods of zinc oxide minerals which have been proposed in the literature have been detailed with the aim of identifying the important factors involved in the flotation process. The various aspects of recovery of zinc from these minerals are also dealt with here. The literature indicates that the collector type, sulfidizing agent, pH regulator, depressants and dispersants types, temperature, solid pulp concentration, and desliming are important parameters in the process. The range and optimum values of these parameters, as also the adsorption mechanism, together with the resultant flotation of the zinc oxide minerals reported in the literature are summarized and highlighted in the paper. This review presents a comprehensive scientific guide to the effectiveness of flotation strategy.