Chaobo Tang

Dissolution kinetics of low grade complex copper ore in ammonia-ammonium chloride solution

The leaching kinetics of Tang-dan refractory low grade complex copper ore was investigated in ammonia-ammonium chloride solution. The concentration of ammonia and ammonium chloride, the ore particle size, the solid-to-liquid ratio and the temperature were chosen as parameters in the experiments. The results show that temperature, concentration of ammonia and ammonium chloride have favorable influence on the leaching rate of copper oxide ores. But, leaching rate decreases with increasing particle size and solid-to-liquid ratio. The leaching process is controlled by the diffusion of the lixiviant and the activation energy is determined to be 23.279 kJ/mol. An equation was also proposed to describe the leaching kinetics.

Extraction of indium from indium-zinc concentrates

Abstract A new process for extracting indium from indium-zinc concentrates was proposed. The process can directly extract indium from removed copper solution by D2EHPA, and cancel the stage of removing iron in the traditional process because of using iron and part of zinc in the In-Zn concentrates for direct preparing high quality Mn-Zn soft magnetic ferrites. The technologies in the processes, such as leaching the neutral leached residues with high concentrated acid at high temperature, reduction ferric and removing copper, and extracting indium, were investigated. The results show that total recovery ratio of indium is increased from less than 70% in the traditional process to more than 95%. This process has the advantages of largely simplifying the procedure of indium extraction, zero draining off of iron residue and zero emitting of SO2. So this is a clean production process.

Heavy metal removal and crude bio-oil upgrade from Sedum alfredii Hance harvest using hydrothermal upgrading.

In this study, heavy metals were removed and crude bio-oil was yielded from a heavy metal hyperaccumulator harvest, Sedum alfredii Hance, through hydrothermal upgrading process. This paper reports on the optimization of process parameters for the removal of heavy metals (zinc, lead, and copper) and for the upgrading of crude bio-oil from this biomass in an autoclave. Parameters such as granularity, temperature, pressure, and duration were examined for their effect on the removal efficiency of heavy metals and upgrading efficacy of crude bio-oil. Maximum heavy metal removal efficiency of >99% and crude bio-oil upgrading efficiency of >60% were attained with an 18 mesh (1 mm) granularity, and 22.1 MPa at 370 degrees C in the presence of 10 mg/L additives (K(2)CO(3)) for 60 s. Under these optimized conditions, an oil phase (mostly composed of phenolic hydrocarbons and derivatives), a water phase raffinate (containing Zn(2+) (0.39 g/L), Pb(2+) (0.10 g/L), Cu(2+) (0.15 g/L)), and a solid phase (the hydrothermal upgrading residue, which completely satisfies the limit set by China legislation related to biosolids disposal) were obtained.

Recovery of zinc from hyperaccumulator plants: Sedum plumbizincicola

Hyperaccumulator biomass harvested after heavy‐metal phytoremediation must be considered as hazardous waste that should be contained or treated appropriately before disposal or reuse. As a potential method to detoxify the biomass and to convert this material to a suitable fertilizer or mulch, leaching of heavy metals from Sedum plumbizincicola biomass was studied by using ammonia–ammonium chloride solution as a leaching agent. The research was carried out in two phases: (i) a leaching study to determine the heavy metal:zinc extraction efficiency of this leaching agent and (ii) a thermodynamic analysis to identify the likely reactions and stable Zn(II) species formed in the leaching systems. Experimentally, a Taguchi orthogonal experiment with four variable parameter elements: leaching temperature, nNH4Cl:nNH3 ratio, leaching time and solid–liquid ratio, each at three levels, was used to optimize the experimental parameters by the analysis of variances. Application of the Taguchi technique significantly reduced the time and cost required for the experimental investigation. The findings indicate that leaching temperature had the most dominant effect on metal extraction performance, followed by nNH4Cl:nNH3 ratio, solid–liquid ratio and leaching time. Accordingly, the optimum leaching conditions were determined as temperature: 60°C, nNH4Cl:nNH3 = 0.6, leaching time: 2 h and solid/liquid ratio: 5:1. The total zinc removal after leaching under the optimum conditions reached 97.95%. The thermodynamic study indicated that the dominant species produced by the leaching process should be the soluble species Zn(NH3)4 2+.

Thermal solidification of stainless steelmaking dust

Abstract Stainless steelmaking dust makes an environmental problem in the disposal or landfills and has been assigned as a hazardous waste by various government regulatory agencies because it leaches heavy metals to the groundwater or rainwater in the concentrations exceeding the environmental guidelines for solid waste disposal. Solidification of the dust is to stabilize the hazardous components into amorphous silica-alumina-based clays. Various mixtures of stainless steelmaking dust and clay were investigated and the softening temperatures of these mixtures were measured. The results indicate that the mixture of stainless steelmaking dust and clay additive with 1:1 ratio has the lowest softening temperature of 1 100 °C. The clinkers can pass the TCLP leaching test after being thermally treated at the softening temperature for 15 min. A thermal process for the solidification of stainless steelmaking dust with typical clay is developed and the product is desirable for the production of bricks or disposal and landfill.

Thermodynamics of solubility of Cu2(OH)2CO3 in ammonia-ammonium chloride-ethylenediamine(En)-water system

Abstract In order to decrease the evaporating rate of ammonia and increase the solubility of copper in the solution, ethylenediamine was added into the ammonia-ammonium chloride system to leach the copper-containing oxide ores. The thermodynamic model was constructed and the solubility of malachite Cu 2 (OH) 2 CO 3 in the ammonia-ammonium chloride-ethylenediamine(En)-water system was calculated using the exponential computation method based on both mass balance and charge balance. It is found that the solubility of copper can be increased and the free ammonia concentration can be decreased by submitting partial ammonia with ethylenediamine. The lower free ammonia concentration in the solution is a guarantee to the lower evaporating rate of ammonia. The conditions of malachite Cu 2 (OH) 2 CO 3 converting to atacamite Cu(OH) 1.5 Cl 0.5 were also studied. A group of experiments were designed to validate the veracity of the results of the thermodynamic calculation. It is found that the thermodynamic model is reliable and it can guide the leaching process.

Zinc removal from hyperaccumulator Sedum alfredii Hance biomass

Abstract Leaching of heavy metals from Sedum alfredii Hance biomass was studied with ammonia-ammonium chloride solution as leaching agent. The research was carried out in two phases: 1) a leaching study to determine the zinc extraction efficiency of this leaching agent, and 2) a thermodynamic analysis to identify the likely reactions and stable Zn(II) species formed in the leaching systems. Taguchi orthogonal experiment, with four variable parameters, leaching temperature, molar ratio of NH 4 Cl to NH 3, leaching time and solid-to-liquid(L/S) ratio, and each at three levels, was used to optimize the experiment parameters by the analysis of variances. The results indicate that leaching temperature has the most dominant effect on metal extraction performance, followed by molar ratio of NH 4 Cl to NH 3 , solid-to-liquid ratio and leaching time. The optimum condition was obtained as follows: temperature of 60°C, molecular ratio of NH 4 Cl to NH 3 of 0.6, leaching time of 2 h and solid-to-liquid ratio of 5:1. The total zinc leaching efficiency under optimum conditions reaches 97.95%. The thermodynamic study indicates that the dominant species produced by the leaching process should be the soluble Zn(NH 3 ) 42 + .

Environmental risk assessment on slag and iron-rich matte produced from reducing-matting smelting of lead-bearing wastes and iron-rich wastes

Abstract A new process for utilization of hazardous lead-bearing wastes and iron-rich wastes by reducing-matting smelting has been developed. The slag (SG) and the iron-rich matte (IRM) are the main by-products from reducing-matting smelting of lead-bearing wastes and iron-rich wastes. The environmental risk of heavy metals (Cd, Zn, Pb and As) in the main by-products versus the charging material for reducing-matting smelting (CM) has been systematically assessed using leaching toxicity test, the three-stage sequential extraction procedure of European Community Bureau of Reference (BCR) and Hakanson Potential Ecological Risk Index Method (PERI). The results demonstrate that the ecological risk level of heavy metals for SG and IRM is significantly reduced after the reducing-matting smelting process compared with that for CM.

Leaching kinetics of zinc silicate in ammonium chloride solution

Abstract The leaching kinetics of zinc silicate in ammonium chloride solution was investigated. The effects of stirring speed (150–400 r/min), leaching temperature (95–108 °C), particle size of zinc silicate (61–150 μm) and the concentration of ammonium chloride (3.5–5.5 mol/L) on leaching rate of zinc were studied. The results show that decreasing the particle size of zinc silicate and increasing the leaching temperature and concentration of ammonium chloride can obviously enhance the leaching rate of zinc. Among the kinetic models of the porous solids tested, the grain model with porous diffusion control can well describe the zinc leaching kinetics. The apparent activation energy of the leaching reaction is 161.26 kJ/mol and the reaction order with respect to ammonium chloride is 3.5.

Reductive smelting of spent lead–acid battery colloid sludge in a molten Na2CO3 salt

Lead extraction from spent lead–acid battery paste in a molten Na2CO3 salt containing ZnO as a sulfur-fixing agent was studied. Some influencing factors, including smelting temperature, reaction time, ZnO and salt dosages, were investigated in detail using single-factor experiments. The optimum conditions were determined as follows: T = 880°C; t = 60 min; Na2CO3/paste mass ratio = 2.8:1; and the ZnO dosage is equal to the stoichiometric requirement. Under the optimum conditions, the direct recovery rate of lead reached 98.14%. The results suggested that increases in temperature and salt dosage improved the direct recovery rate of lead. XRD results and thermodynamic calculations indicated that the reaction approaches of lead and sulfur were PbSO4→Pb and PbSO4→ZnS, respectively. Sulfur was fixed in the form of ZnS, whereas the molten salt did not react with other components, serving only as a reaction medium.