Aiqun Yuan

This study focused on the exploration of a novel reductive leaching method from pyrolusite ore which can effectively reduce residual organics in leaching solution. Formaldehyde was used as a reductant to extract manganese from low-grade pyrolusite. Organic residue in the leaching solution was analyzed via HPLC. Kinetics model was also exposed. The optimized leaching conditions were as follows: H₂SO₄ concentration 2.21 mol/L, liquid-to-solid ratio 8:1, 2.5 ml formaldehydel/10g low-grade pyrolusite, stirring rate 200 r/min, leaching temperature 353 K and leaching time 120 min. The extraction ratios of Mn, Al, Fe, Mg, and Ca were 90.24%, 22.78%, 61.61%, 53.38%, and 84.2%, receptively under the optimized conditions. Formic acid was the main residual organic from the oxidized production of formaldehyde; its concentration was only 2.24 g/L. The kinetic data for leaching process obeyed a mix-controlled kinetic model. The apparent activation energy of leaching reaction was 34.81 kJ/mol for 0-30min, 30.1 kJ/mol for 30–150min, respectively.

Catalysts of aluminum dihydrogen tripolyphosphate supported by activated carbon ((ATP-AC) were prepared by using activated carbon oxidized by Na₂S₂O₈, H₂O₂ and HNO₃, respectively, and characterized by Brunauer-Emmett-Teller (BET), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscope (FE-SEM) and X-ray diffraction (XRD). The orthogonal design experiment was used to obtain the best condition of the three kinds of catalysts. The results show that the three kinds of ATP-AC catalyst disply higher activity and selectivity. The optimal conditions are: for preparation conditions of catalyst ATP-AC-1: oxidant concentration c (Na₂S₂O₈) = 0.75 mol/L, bonding temperature t = 603 K, mass ratio W% (ATP) = 60%; for catalyst ATP-AC-2: oxidant concentration c(H₂O₂) = 1.0 mol/L, bonding temperature t = 603 K mass ratio W% (ATP) = 60%; for catalyst ATP-AC-3: oxidant concentration (HNO₃) = 0.5 mol/L, bonding temperature t = 603 K, mass ratio W% (ATP) = 60%. The yield of tributyl citrate is over 90%. Three kinds of oxidants increase the carbon-oxygen functional groups of activated carbon and improve its hydrophilicity. The pore structure of oxidated AC is more regular, and the quantity of microporous and larger pores is increased. All these changes promote the chemical bonding between activated carbon and ATP.

Ammonium-iron(III) bis(hydrogenphosphate) was synthesized via solid-state reaction at low temperature and characterized by X-ray diffraction, infrared spectroscopy and scanning electron microscope. Standard molar enthalpy of formation was determined by an isoperibol solution calorimeter at 298.15K. The results show that the obtained product is NH₄Fe(HPO₄)₂ with shape of Lamellar particles. According to Hess's law, a new thermochemical cycle was designed, and the standard enthalpy of formation of the titled complex at 298.15K is: Δ_fH_m^φ[(NH₄)Fe(HPO₄)₂ (s), 298.15K] = −2641.52 ±0.06 kJ·mol⁻¹.

Potassium zinc phosphate was synthesized by solid-state reaction using K₃PO₄·3H₂O and ZnSO₄·7H₂O as reagents. To investigate the influence of molar ratio, grinding time, holding temperature, holding time on yield and zinc content of the product, experimental project was designed by uniform design and data mining technology. Obtained product was characterized by X-ray diffraction, scanning electron microscope and energy disperses spectroscopy. The results show that the two mathematical models can be established by regression analysis according to yield and zinc content, which can be used to obtain the best technology conditions of solid-state reaction. Under the optimum reaction conditions: molar ratio of K₃PO₄·3H₂O: ZnSO₄·7H₂O = 1.01, grinding time 31min, holding temperature 750°C, holding time 3.2 h, the prepared product is KZnPO₄ with nano-lamellar structure, and the reaction average yield value is 84.33% and zinc content is 31.29%.