The Kaolin Pac

Kaolinite of somewhere can't become the raw material of high-grade ceramics because of high content of iron and low white degree. However, it is a low-cost raw material of preparing PAC owing to the certain contents of Al₂O₃ (38.06 %). In this paper, the process and application of preparing polyalurninium chloride by using this kind of kaolinite has been studied, which involved three processes of activation, extraction and polymerization. And the application included studies of the treatment of simulated wastewater and real wastewater by PAC samples. On the basis of laboratory studies, the pilot test and commercial application of products were carried out, especially. The main results obtained are as follows:In the step of activation, the chemical composition and physical phase of the kaolinite ore were analyzed by chemical analysis methods. The morphology and thermal behavior were characterized by scanning electron microscope (SEM) and thermogravimetric-differential scanning calorimeters (TG-DSC) respectively. The crystallization and phase transition of kaolinite under various calcining temperatures were studied with X-ray diffractometer (XRD). The results showed that the typical amorphous substance metakaolin was formed at 700～800℃, and Al-O octahedra sheets were destroyed. Therefore, the activated temperature of inert Al₂O₃ ranges from 700 to 800℃.In the step of extraction, the effect of the calcining temperature and time, acid-dissolved concentration and proportion, acid-dissolved temperature and time, dosage of excitant on the leaching rate of Al₂O₃ was studied by orthogonal test method. Considering the feasibility and the economic efficiency in actual production, the appropriate process parameters of extracting processes were finally determined as follows: kaolinite was calcined at 750℃for 1 hour; acid-dissolved concentration and proportion are 20 % and 1:6.0, respectively; acid-dissolved temperature at 100℃for 2.0 hours; and dosage of excitant is 3.0g/100g.In the step of polymerization, NaOH,Na₂CO₃ and CaCO₃ were selected as regulators, and their behavior during polymerization and effect on the product indexes were studied. CaCO₃ was finally determined as the regulator for polymerization. The distribution of aluminum species of PAC was studied by Al-Ferron complexation timed spectrophotometry, and the effect of n_Ca/n_Al ratio on stability of liquid PAC was investigated. The results showed that, n_Ca/n_Al ratio had a direct effect on aluminum species in high calcium content system; aluminum species were predominated by the stable species Al_b and the system was relatively stable when the n_Ca/n_Al ratio was low; and with increasing n_Ca/n_Al ratio, however, the species Al_b decreased, while the unstable species Al_c increased, which affects the stability of PAC.The efficiency of treatment for methyl orange simulated wastewater by using the PAC was studied. The results showed that when the dose of flocculant is 4 g and volume of simulated wastewater is 150 mL, the removal rate of colority , turbidity and COD are 67 %, 67 % and 76 %, respectively. Meanwhile, the PAC was diluted to 5 mg/mL (as Al₂O₃) with deionized water and that diluent was used to treat domestic wastewater. When the dose of flocculant is 5 mL and volume of wastewater is 200 mL, the removal rate of colority , turbidity and COD are 96 %, 96 % and 76 %, respectively.The pilot test results suggested that industrial products reaching technical indexes of national standard (GB15892-2003) and fully confirmed the reliability of laboratory technique. The commercial application results indicated the fluctuation range (11.4 FTU) of turbidity of effluent water was below that of present products (20.4 FTU), and the turbidity of effluent water is stable.