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Flower-like ZnO microstructures were successfully produced using a hydrothermal method employing ZnSO4/(NH4)2SO4 as a raw material. The effect of the operating parameters of the hydrothermal temperature, OH−/Zn2+ molar ratio, time, and amount of dispersant on the phase structure and micromorphology of the ZnO particles were investigated. The synthesis conditions of the flower-like ZnO microstructures were: hydrothermal temperature of 160°C, OH−/Zn2+ molar ratio of 5:1, reaction time of 4 h, and 4 mL of dispersant. The flower-like ZnO microstructures were comprised of hexagon-shaped ZnO rods arranged in a radiatively. Degradation experiments of Rhodamine B with the flower-like ZnO microstructures demonstrated a degradation efficiency of 97.6% after 4 h of exposure to sunshine, indicating excellent photocatalytic capacity. The growth mechanism of the flower-like ZnO microstructures was presented.

NH4HCO3 conversion followed by HCl leaching was performed and proven to be effective in extracting Pb and Sr from zinc extracted residual. The mechanism and operating conditions of NH4HCO3 conversion, including molar ratio of NH4HCO3 to zinc extracted residual, NH4HCO3 concentration, conversion temperature, conversion time, and stirring velocity, were discussed, and operating conditions were optimized by the orthogonal test. Experimental results indicate that NH4HCO3 conversion at temperatures ranging from 25 to 85°C follows the shrinking unreacted core model and is controlled by inner diffusion through the product layer. The extraction ratios of Pb and Sr under optimized conditions reached 85.15% and 87.08%, respectively. Moreover, the apparent activation energies of Pb and Sr were 13.85 and 13.67 kJ·mol−1, respectively.

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.

Conventional reduction treatment methods for nickel slag show drawbacks such as high energy cost, heavy material burden or secondary pollution. Thus, a novel environmentally friendly reduction treatment method for high-silicon wastes, especially nickel slag, is proposed in this paper. The main characteristic is to lower the alkali–ore ratio (mass ratio of NaOH to ore) through introducing a high-speed premixing procedure before roasting. Optimal process parameters have been found experimentally, i.e., a roasting temperature of 823 K, alkali–ore ratio of 1.6:1, and roasting time of 30 min. The desilication ratio reached to 91.3 wt.%. Compared with previous NaOH roasting processes with stirring, the NaOH consumption is down by 60%, which greatly reduces the material burden. Through carbonation decomposition of the Na2SiO3 solution generated in the NaOH roasting, amorphous silica is recycled as the final product. The proposed method is expected to be a promising method for industrial reduction treatment of nickel slag.

ZnO@SiO2 composite with flower-like structure was successfully prepared with molar ratio of ZnO/SiO2 = 1:1 based on the optimized synthesizing parameters of spherical SiO2 and flower-like ZnO. SiO2 particles were coated on the flower-like ZnO to form a homogeneous film through the multidimensional polycondensation of Si(OH)4. The photocatalytic degradation ability of ZnO@SiO2 composite for rhodamine B (RhB) obtained at different ZnO/SiO2 molar ratio and the comparison to that of flower-like ZnO showed that ZnO@SiO2 composite with ZnO/SiO2 molar ratio of 1:1 displayed a relatively good photocatalytic degradation ability to degrade RhB, but it was weaker than that of flower-like ZnO. Twenty millilitres of RhB solution at a concentration of 15 mg·L−1 could be completely degraded by 300 mg flower-like ZnO powder within 3 h, while the degrading efficiency was only 82.5% by 300 mg ZnO@SiO2 composite. But ZnO@SiO2 composite showed a better photocatalytic activity than flower-like ZnO at a lower pH value of 4.5.

High iron content is one of the challenges in utilizing the refractory bauxites in China. An improved method for treating the high-iron bauxite by roasting with (NH4)2SO4 was proposed, which offers a possible alternative method for utilizing the high-iron bauxite. The influences of the roasting time, roasting temperature, material ratio, and ore particle size on the extraction ratios of Fe and Al were studied, and the orthogonal test was used to optimize the reaction conditions. The optimized reaction conditions were proposed as follows: roasting temperature of 450 °C, roasting time of 120 min, material ratio of (NH4)2SO4 to ore of 2.5:1.0, and ore particle size below 80 μm. The roasting mechanism and kinetic parameters including the apparent activation energy and reaction rate constant were investigated. The results showed that the control step of the roasting process was the internal diffusion on the product layer and the apparent activation energy was 19.22 kJ mol−1 in the reaction temperature range. The kinetic equation was obtained finally.

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.

A novel process was developed for the preparation of ultrafine silica from potash feldspar. In the first step, potash feldspar was roasted with Na2CO3 and was followed by leaching using NaOH solution to increase the levels of potassium, sodium, and aluminum in the solid residue. The leaching solution was then carbonated to yield ultrafine silica. The optimized reaction conditions in the roasting process were as follows: an Na2CO3-to-potash feldspar molar ratio of 1.1, a reaction temperature of 875°C, and a reaction time of 1.5 h. Under these conditions, the extraction rate of SiO2 was 98.13%. The optimized carbonation conditions included a final solution pH value of 9.0, a temperature of 40°C, a CO2 flow rate of 6 mL/min, a stirring intensity of 600 r/min, and an ethanol-to-water volume ratio of 1:9. The precipitation rate and granularity of the SiO2 particles were 99.63% and 200 nm, respectively. We confirmed the quality of the obtained ultrafine silica by comparing the recorded indexes with those specified in Chinese National Standard GB 25576―2010.

The ZnO powder was successfully obtained by calcining the basic zinc carbonate, which was synthesized from clinker digestion solution of zinc oxide ore using analytical Na2CO3. The factors of mol ratio of Na2CO3to ZnSO4and reaction temperature were discussed at stirring intensity 400 rpm. Both the obtained basic zinc carbonate and ZnO powders were characterized using XRD, EDS and SEM. The thermal decomposition of basic zinc carbonate was also investigated below 600°C. The results show that the ZnO powder was wurzite hexagonal structure and the well-crystallized ZnO powder was uniformly spherical particles and distributed in a narrow range.

Na2SO4solution that was obtained from ZnSO4solution after Zn2+precipitation using Na2CO3was used as raw material. The Na2SO4·7H2O crystallization was obtained through cooling the Na2SO4solution, and then the solution was cycled. The Na2SO4·7H2O was dried and then put into a porcelain boat located in a roaster. When the reaction between Na2SO4and CO ended, the Na2S was obtained. The influences of reaction temperature, reaction time and material thickness on the conversion rate were discussed. The appropriate reaction conditions were reaction temperature 675°C, reaction time 120min and material thickness less than 4cm.

Ultrafine ZnO powder was synthesized by precipitation method, using zinc sulfate and aqueous ammonium carbonate as raw material and precipitant, respectively. The influence of the concentration of aqueous ammonium carbonate on the precipitation rate of Zn2+ was discussed and their relationship was also illustrated. The precipitation rate of Zn2+ increased gradually with the mol ratio of CO32-to Zn2+, which reached up to more than 96% when the mol ratio was 1.2. In addition, the crystal structure and morphology of the precursor and ZnO powder were also characterized using XRD and SEM. The results indicated that ZnO powder was hexagon wurtzite structure and spherical figure with high purity and regular crystal form.

With zinc acetate used as raw material and polyethylene glycol employed as dispersant, ultrafine ZnO flower-like powder was successfully synthesized by hydrothermal method using NaOH and NH3·H2O as precipitants. The influences of the precipitants on the morphology of the ZnO powder were discussed. The as-synthesized ZnO flower-like powder was composed of lots of microrods with hexagon figure. The ZnO flower-like structures synthesized using NaOH were more regular and uniform than that obtained using NH3·H2O. The ZnO flower-like powder was hexagonal wurtzite structure with high purity. The exciton absorptions of the two ZnO flower-like powder both appeared at 300 nm in UV-VIS spectrum.

With zinc acetate and sodium hydroxide used as raw materials, while polyethylene glycol employed as dispersant agent, ultrafine zinc oxide flowers were successfully synthesized by hydrothermal method. The influence of the concentration of PEG20000 on the morphologies of ZnO flowers was discussed. The as-synthesized ZnO flowers consisted of microrods with hexagonal morphologies. The crystal structure and ultraviolet absorbing performance of ZnO flowers were also characterized using XRD, UV-VIS absorption spectrum. The results indicate that ZnO flowers are hexagonal wurtzite structure with high purity. There is a strong excition absorption peak at 300 nm in UV-VIS absorption spectrum and blue shift existed obviously.