Application of cupric or ferric ions as environmentally benign oxidants to the chloride leaching of platinum from spent reforming catalysts.

Recovery of precious metals has been considered due to their limited availability and resources, and the reduction of environmental hazards. In this study, the environmentally friendly chloride leaching method was used to recover platinum (Pt) from a spent reforming catalyst. Hydrochloric acid and sodium chloride were applied as the complexing agent and ferric or cupric chloride (FeCl3, CuCl2) was used as oxidants. Response surface methodology was implemented to investigate the influences of acid concentration (1-3 M), oxidant concentration (0.5-1.3 M), and temperature (70-90 °C) on the Pt extraction at a fixed duration of 3 h using two separate Box-Behnken experimental designs. Increasing temperature and acid concentration improved the Pt recovery from ∼52% to ∼89% in the presence of 1 M FeCl3, and from ∼29% to 94% in the presence of 0.75 M CuCl2. Generally, at low acid concentrations, ferric chloride was more efficient in Pt dissolution, while, at high acid concentrations, cupric chloride performed better. Finally, the platinum content of the pregnant leach solution was precipitated by adding a saturated ammonium chloride solution. According to the results of the X-ray diffraction analysis, the obtained precipitate was mainly composed of ammonium hexachloroplatinate, sodium chloride, and ammonium chloride. Also, the Pt assay of the powder was determined as 21%.

Evolving multilayer perceptron, and factorial design for modelling and optimization of dye decomposition by bio-synthetized nano CdS-diatomite composite.

Design of experiment and hybrid genetic algorithm optimized multilayer perceptron (GA-MLP) artificial neural network have been employed to model and predict dye decomposition capacity of the biologically synthesized nano CdS diatomite composite. Impact of independent variables such as, light (UV: on-off), solution pH (5-8), composite weight (CW: 0.5-1 mg), initial dye concentration (DC: 10-20 mg/l) and contact time (0-120 min), mainly in two levels, were examined to evaluate dye removal efficiency of the composite. According to the developed response surface based on the factorial design, all independent variables shown positive interactive effect on dye removal (UV > CW > pH > DC), as well as the pH-CW mutual interaction, while both UV-DC and CW-DC had antagonistic effect. The pH-CW interaction was more influential than pH and DC. Incorporation of the intermediate measurements of dye removal between the start and final contact times in GA-MLP approach, had found to improve the accuracy and predictability of the GA-MLP model. Based on the closeness of the R2 (0.98), root mean square error (1.03), variance accounted for (98.23%), mean absolute error (0.61) and model predictive error (9.46%) to their desirable levels, proposed GA-MLP model outperformed the factorial design model. Finally, optimal parameter choice for maximum dye removal using factorial design and GA-MLP were found as: UV (on), pH (9), CW (1 g) and DC (10 mg/l) and UV (on), pH (8.85), CW (0.92 g), DC (12.3 mg/l) and T (117 0.6 min), respectively.

Kinetics, isotherm, and optimization of the hexavalent chromium removal from aqueous solution by a magnetic nanobiosorbent.

Sorption is the most effective approach to the treatment of acid mine drainage (AMD) and wastewaters, but the removal of the adsorbents from water has always been a challenging problem which may be resolved by using magnetic separation. In this work, a magnetic bioadsorbent was prepared using low cost and high-performance sources and applied in Cr(VI) removal from a synthetic solution. Initially, magnetite nanoparticles were synthesized from iron boring scraps by chemical co-precipitation method. Results of dynamic light scattering (DLS) and vibrating sample magnetometry (VSM) analyses showed that the synthesized nanoparticles were around 40 nm in size and had a significant magnetization. Then, the magnetite nanoparticles were attached to the dead and alkaline activated biomass of Aspergillus niger. Central composite design (CCD) was applied to determine the optimal condition of Cr(VI) adsorption on the produced magnetic nanobiocomposite. The maximum chromium removal (~ 92%) was achieved at pH 5.8, Cr concentration 23.4 mg/l, adsorbent dose 3.72 g/l, agitation rate 300 rpm, and duration 11 min. Kinetic studies showed that regardless of temperature, the process was controlled by mass transfer and intraparticle diffusion with an equilibrium constant of 0.74 mg/g min1/2 at 40 °C. Also, the adsorption isotherms followed the Temkin model, which indicated the physical adsorption of Cr(VI) on the produced sorbent. Therefore, the magnetic nanobiocomposite has a perfect ability to be used as the chromium adsorbent and can be collected by a low external magnetic field. Graphical abstract Synthesis of the magnetic nanobiosorbent and its application in the removal of Cr(VI) from wastewaters.

From the iron boring scraps to superparamagnetic nanoparticles through an aerobic biological route.

A straightforward, highly efficient, and low-cost biological route was introduced for the synthesis of magnetic nanoparticles. Three urease-positive bacteria namely, Bacillus subtilis, B. pasteurii, and B. licheniformis were used to biosynthesize ammonia and biosurfactants required for the nanoparticle production. Also, the features of the applied biological approach was compared with a chemical co-precipitation method. X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), dynamic light scattering (DLS), vibrating-sample magnetometer (VSM), and Fourier transform infrared spectroscopy (FTIR) were applied to characterize the synthesized nanoparticles. Results indicated that the biologically fabricated powders had a single domain structure, and their mean particle size was in the range of 37 to 97 nm. The production capacity of the biological processes was double the chemical method, and the biosynthesized superparamagnetic nanoparticles had higher saturation magnetization up to 132 emu/g. Finally, the removal of Cr(VI) from a synthetic solution was investigated using the four products. The maximum elimination of chromium (over 99%) was achieved by the particles synthesized by B. pasteurii, with the adsorption capacity of 190 mg/g.

Synthesis of CdS nanoparticles from cadmium sulfate solutions using the extracellular polymeric substances of B. licheniformis as stabilizing agent.

Mining and hydrometallurgical industries produce large amounts of hazardous metal sulfate solutions as a by-product which can be recycled and exploited to produce valuable and advanced materials. Here, for the first time, extracellular polymeric substances of Bacillus licheniformis were applied as biosurfactants to synthesize quantum dots of cadmium sulfide from pure artificial and impure industrial cadmium sulfate solutions. The bacterial biopolymers stabilized the generated crystalline nuclei as colloidal dots and prevented their further growth or agglomeration. In order to discover the composition and size distribution of the produced particles, characterization was performed by X-ray diffraction (XRD), and transmission electron microscopy (TEM). Results showed that the particles biosynthesized from the pure solution were nano-sized cubic crystals of CdS with the dimensions of 2-10nm. The same product was also derived from the impure industrial solution. The outcomes of this study indicate the feasibility of cadmium or probably other metal recovery from industrial solutions and wastewaters in the form of valuable metal sulfide nanoparticles.