| Calcium sulfate whisker is a kind of inorganic fiber crystal with good over-all performance, which has been widely applied in fields such as latex, plastic, friction material, and flame resistant material. Former research indicated that calcium sulfate whisker can be used as filter and adsorption material, but facing the problems such as low affinity with heavy metals and unstable properties, limiting its direct application. Hence, it is necessary to study the synthesis method and performance improvement, which is significant for fully utilization of gypsum resources in China.Firstly, we studied the preparation of HH whisker with uniform morphology by normal pressure salt solution method using DH as raw material, mainly discussing effects of the factors such as sulfuric acid concentration, chloride calcium concentration, temperature, speed, and sulfate dihydrate calcium mass percentage on HH formation process. Combining with the tests of morphology and crystal water content, the optimum conditions for the preparation of the HH whisker was determined. The results showed that with 0.1 OM sulfuric acid,3.0M calcium chloride, a reaction temperature of 95?,10%DH mass percentage, and a sirring speed of 200r/min, whisker products with uniform morphology and even particle size could be obtained with fast transformation. The HH whisker achieved at 120min has a BET surface area of 60.92m2/g and an average pore size of 1.84nm. The transformation process of DH is through a dissolvation-recrystallization process.Secondly, we investigated the effects of the arsenic adsorption properties of HH whisker modified with sodium phosphate-copper composite modifier, focusing on the effects of modification reaction time, temperature, pH, the concentration of copper chloride, and sodium phosphate concentration. The results show that the arsenic adsorption efficiency of HH whisker generally increases with the modification time but decreases when the modification reaction goes beyond 12h. The arsenic adsorption efficiency of HH whisker firstly increases with pH and then decreases. Higher temperature and copper chloride concentration will promote the performance of HH whisker. The performance will decrease with the increase of sodium phosphate concentration when it is above 5mM. Under the condition of pH=9.0?60?? copper chloride concentration= 20mM, concentration of sodium phosphate=5 mM, HH suspension concentration= lOg/L, reaction time=3h, HH whisker with an arsenic adsorption efficiency of more than 95% can be obtained.In addition, the modified conditions were optimized by P-B design and BBD experiment and a quadratic equation model was obtained for whisker's arsenic removal ability. The response surface analysis of two factor interaction on arsenic adsorption efficiency showed that arsenic removal rate of the whisker increased with the concentration of copper chloride and decreased with the increasing of the concentration of sodium phosphate, when the pH value increases, arsenic removal rate increased at first and reduce thereafter. The optimum experimental conditions is: the concentration of copper chloride=11.18mM, concentration of sodium hypophosphite=0.72mM, pH=7.3, temperature=60?, reaction time=5h.The arsenic removal rate of the modified whisker is up to 96.68%. According to the XRD analysis, calcium arsenic was detected, indicating that arsenic may form deposits on the surface of whiskers. |
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