Reutilization Of Waste Lcd Screen Polishing Liquor

Along with the rapid development of LCD technology, the amount of LCD screen polishing waste liquor is also increasing. LCD screen polishing waste liquor contains higher concentration of hydrofluoric acid, fluorosilicate acid and sulfuric acid, which can cause great harm to human, animals and plants. The harmless disposal ways of waste containing fluorine have been undertaken extensive researches by domestic and overseas scholars, and the technology is more mature. The harmless disposal ways not only produce large amount of fluorine-containing sludge, but also produce a potential threat to the environment. Now, fluorine-containing sludge is difficult to recyle. Reutilization research of LCD screen polishing waste liquid has rarely been reported. This paper explored a new technology for recycling the SiF62-and F-,which achieved effective recovery fluorine resources and protected the environment.The first step, the sodium carbonate method, sodium chloride method, and potassium chloride method for recycling SiF62-of the LCD screen the polishing waste liquid were researched. Compared with the advantages and disadvantages of three methods, the sodium carbonate method became the best choice. The experimental results showed that:the sodium carbonate method could effec(?)avely recyle the SiF62-, and obtain the preparation of sodium fluorosilicate. The optimal condition of recycling SiF62-was as following:the concentration of SiF62-was39.63g·L-1, the reaction time was30minute, and sodium carbonate dosage was theory demand value’s200%. Under these conditions, fluorine silicate ions recovery rate was94.31%and the prepared sodium fluorosilicate can meet the quality standard of HG/T3252-2000.The second step, the continuous process and stepwise synthesis process of preparaed cryolite were researched, which used NaOH and NaAlO2mixed solution and the filtrate from the first step experiment. The continuous process was the best choice on the basis of the comparison effect of two processes. NaOH and NaAlO2mixed solution was added into the filtrate from the first step experiment by the continuous process, which generated cryolite. The appropriate reaction condition of preparing cryolite was as following:temperature was80℃, n(F):n(Na) was5.4, mass fraction of NaOH and NaAlO2was20%, n(Na):n(Al) was3.4. Under these conditions, the n(Na):n(Al) of the prepared cryolite was2.84, which met the quality standard of GB4291-2007for CH-l.The recovery rate of fluoride ion reached at93.73%. Cryolite product was characterized by XRD and SEM, and the results showed that the cryolite was high purity, no significant impurities and larger particles.At last step, removing methods of fluoride in filtrate which came from the prepared cryolite process were researched. The calcium hydroxide treatment method was put forward. The optimum condition was as following:pH of the reaction solution was7.03, n(Ca):n(F) of reaction system was2.0. Under these conditions:the concentration of fluoride droped to7.33mg·L-1, which was less than10mg·L-1and met requirement of industrial wastewater emission standard.