Study On Purification Of Aphanitic Graphite Using Fluoride-Hydrochloric Method

In order to improve the added value of aphanitic graphite and expand its industrial applications, the paper studied the purification process of aphanitic graphite which comes from Chenzhou Hunan and has the fixed carbon content of 83.08%.The main content of the study is listed as below,1.Purification of aphanitic graphite:dosage of fluoride, amount of hydrochloric acid、 reaction temperature、reaction time and reaction times’s effects on aphanitic graphite’s fixed carbon content, while choosing ammonium fluoride and sodium fluoride as orginal material, were studied by using orthogonal experiment in order to optimism the purification process. XPS、XRD and SEM/EDS were choosed to characterize aphanitic graphite’s composition、 micro-structure and phase, and help make a preliminary study to the purification mechanism. The results show,(1) Aphanitic graphite can be purified by sodium fluoride and hydrochloric acid. The fixed carbon content increases with sodium fluoride dosage and liquid-solid ratio, but tended to remain while continuously increase the reaction temperature or reaction time. With the sodium fluoride dosage of 13.5g,solide-liquid ratio of 3:1,reaction temperature of 70℃ and reaction time of 2.5h,aphanitic graphite can be purified with a fixed carbon content of 98.37%.(2) Ammonium fluoride and hydrochloric can effectively pure aphanitic graphite. The fixed carbon content increases with ammonium fluoride dosage percent and reaction times, but decreases with soiled-liquid ration and reaction temperature. The optimized process is: ammonium fluoride dosage percent of 50%,solide-liquid ratio of 2:1 and reaction temperature of 80℃, and the fixed carbon content is 99.04% using this purification process.(3) Characterizations show that most impurities can be removed by fluoride-hydrochloric method, silicate mineral impurities react with fluoride-hydrochloric system to give some water-soluble products which can be wash out afterwards. Fluoride-hydrochloric method will do no harm to aphanitic graphite’s crystal structure and microstructure.2. Treatment of the acidic fluoride-containing wastewater:the study use calcium hydroxide precipitation method to treat the wastewater. Effects of the amount of calcium hydroxide, wastewater’s pH, stirring reaction time and settling time on the fluoride removal efficiency were studied, and the results show that the mass concentration of F increases with calcium hydroxide’s amount, but decreases after the first increasement with pH. The optimized process is:calcium hydroxide’s amount is 5.39g/100mL,pH is 8,stirring time is 10 min. F" mass concentration is less than 10mg/mL, F- removal efficiency is more than 99%,and the final water’s pH maintained at 7 to 8; calcium hydroxide is the precipitant and neutralizer in the treatment process.This paper can provide theoretical guidance for the industrial production of high-purity aphanitic graphite.