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Employing zinc sulfate solution obtained from zinc oxide ore as raw material, sodium hydroxide as precipitant and PEG20000 as dispersant, ultrafine ZnO powders with different morphologies were successfully synthesized through hydrothermal method. The influences of the dosage of PEG20000 solution, molar ratio of OH−/Zn2+, reaction temperature, reaction time and Zn2+ concentration on the structures and morphologies of the ZnO powders were discussed in detail. The reaction conditions of synthesizing ZnO powders with flower-like structure were obtained as below: dosage of PEG20000 with 10% mass fraction 5 mL, molar ratio of OH− to Zn2+ 5, reaction temperature 150 °C, reaction time 8 h at Zn2+ concentration 1 mol L−1. The growth mechanism of ZnO particles with different morphologies was proposed. The ZnO powder with flower-like structure are composed of multiple micro-rods with hexagon morphology and has good photocatalytic degradation ability to degrade RhB. 20 mL RhB solution with 15 mg L−1 could be completely degraded over flower-like ZnO powder 300 mg within 3 h.

The reaction kinetics of roasting zinc silicate using NaOH was investigated. The orthogonal test was employed to optimize the reaction conditions and the optimized reaction conditions were as follows: molar ratio of NaOH to Zn2SiO4 of 16:1, reaction temperature of 550 °C, and reaction time of 2.5 h. In order to ascertain the phases transformation and reaction processes of zinc oxide and silica, the XRD phase analysis was used to analyze the phases of these specimens roasted at different temperatures. The final phases of the specimen roasted at 600 °C were Na2ZnO2, Na4SiO4, Na2ZnSiO4 and NaOH. The reaction kinetic equation of roasting was determined by the shrinking unreacted core model. Aiming to investigate the reaction mechanism, two control models of reaction rate were applied: chemical reaction at the particle surface and diffusion through the product layer. The results indicated that the diffusion through the product layer model described the reaction process well. The apparent activation energy of the roasting was 19.77 kJ/mol.

(NH4)2SO4 roasting followed by water leaching to process nickel- chromium mixed metal oxidized (MO) ore was investigated. The optimal operating parameters were obtained after determining the influences of the molar ratio of (NH4)2SO4 to mixed oxidized ore, roasting temperature and roasting time on metal extractions. The extraction efficiencies of Ni, Fe, Mg, Al and Cr reached 94.02%, 87.87%, 84.14%, 74.00% and 41.49%, respectively. The transformation of mineral phases during roasting were identified by XRD analysis combining with TG-DTA curves and phases transformation analysis of analytic reagents with (NH4)2SO4. The phase transition process in experimental temperature range can be summarized as: MO to (NH4)2M(SO4)2 to MSO4 and M2O3 to (NH4)3M(SO4)3 to NH4M(SO4)2 to M2(SO4)3 (M is divalent and trivalent metallic element). The work demonstrates an effective process to treat nickel-chromium mixed metal oxidized ores. The reaction mechanism of Fe meets the chemical reaction control mechanism, while the reaction mechanism of Ni, Mg and Al follows the mixed control mechanism of the chemical reaction and diffusion controls.