Preparation Method Of Calcium Sulfate Whisker (CSW) And Exploration Of Its Mercury Removal Performance

Calcium sulfate whisker can be widely used in construction, rubber, environmental treatment and other fields because of its physical and chemical properties. In order to explore CSW's potential value and improve the utilization ratio, this paper was carried out to regulation of CSW morphology and structure through recrystallization process by temperature elevation and hydrothermal with the pretreated samples of dihydrate calcium sulfate. Moreover, this study also studied the purifying effect of mercury in the water solution by CSHW modified with chitosan.Calcium sulfate whisker was prepared by recrystallization process during temperature elevation, and the effects of operation parameters such as the solution pH, temperature range, and oscillation rate on the growth characteristic of whisker were investigated. Moreover, the effects of cetylrimethyl ammonium bromide ?CTAB?, sodium dodecyl sulfate ?SDS?, polyethylene glycol ?PEG6000?, and ethylene diamine ?EDA? as additives on whisker morphology were preliminarily explored. The results show that the growth and morphology of calcium sulfate whisker can be affected in the heating reaction system by all the operation parameters and additives, among which, the solution pH and temperature show the most obvious effects, and SDS distinctively retards the nucleation process. With 7g/L SDS in presence, uniform and rod-like crystals with high crystallinity can be obtained. While most calcium sulfate whiskers grow with morphology of lamellar structure, some whiskers exhibit morphologies similar to polycrystal and epitaxial growth.The preparation of calcium sulfate whisker in the polysaccharide solution through hydrothermal method was also explored in this study. A series of batch experiments had been conducted in order to find the effect of chitosan solution concentration, reaction temperature, reaction time on the whisker morphology and the length to diameter ratio, crystal water content, etc, and to analyze the effect of chitosan on the crystal growth mechanism. The results showed that chitosan concentration in the reaction system was an important parameter for whisker morphology, and the samples are rod and prism hemihydrate calcium sulfate whiskers. The largest diameter and the smallest aspect ratios could be achieved in 3g/L chitosan solution. Most of these products have irregular crack surface or hollow pipe structure, with a layered growth trend. Thermal stability of as-prepared whisker does not improve compared with these prepared under blank condition; Long reaction time ang higher temperature are good for the preparation of uniform rod whisker. We can find that novel tube structure whisker could in solution at pH =3 and 160? for 3hrs of reaction. Chitosan serves as a soft template during the preparation process, A facile method for novel calcium sulfate crystals with tube structure and various aspect ratio via hydrothermal reaction combined with changing chitosan concentration in the solution system was proposed, which is simple, fast, and cost-effective.The study also explored the removal efficiency of mercury by CSHW modified with chitosan through batch tests, the effect of reaction time, solution initial pH, whisker dosage, initial Hg concentration were also studied. Meantime, the mechanism of mercury uptake by modified CSHW was discussed based on adsorption kinetics, isothermal adsorption medel, and analysis of XRD and SEM. It was concluded that pH of the aqueous solution was an important parameter for the Hg removal, and an excellent removal efficiency could be achieved at pH=9.30 for 1.5h and 0.8mg/L^-1mg/L initial Hg concentration. Hg adsorption experimental data on modified CSHW were better described with Freundlich isothermal adsorption model under a wide Hg concentration range of 0.5-4 mg/L. Hg²⁺ adsorpted on the surface of whisker conforms to the pseudo-second order adsorption kinetics model, so this process is mainly a chemisorption process.What this paper has studied exhibited a certain reference value to preparation of whisker with novel morphology and structure and therefore improved its potential application...