Application Of PAM Modified Diatomite To Depuration Of Titanium Dioxide Wastewater

The production of titanium dioxide by sulfuric acid method will discharge a great quantity of waste water and acid, mainly containing free H2SO4, iron salts,suspended solids, organic matter heavy metals and so on, if not being properly handled, will cause great pollution to the environment in the future. Using the traditional processing of lime neutralization treatment to purify titanium dioxide wastewater will cost a lot, the added value of comprehensive utilization products are very low, and the discharged sludge will also bring the problem of secondary pollution.Almost no titanium dioxide plant emissions of waste water, gas and sluge can meet the state emission requirements in China.A few of titanium dioxide plants were forced to stop production or relocate because of environmental problems.Therefore, it is very urgent to research the water quality of wastewater generated by the processing for production of titanium dioxide and to explore effective wastewater treatment processing.Polyacrylamide (PAM) was used to modify diatomite in this research. PAM modified diatomite, an adsorbent with efficient adsorption performance, was created and uesd to deal with wastewater from titanium dioxide plants. The treatment effect and adsorption behavior of uesing PAM modified diatomite to deal with the pollutants such as COD and SS in wastewater was also being discussed in the paper. The results of comparative test show that:(1)Dosage:8g·L-1, reaction time:60min; removal rates of COD and SS in the pretreated water samples by neutralization using diatomite to deal with titanium dioxide wastewater could reach52.32%and61.56%respectively.(2)The removal rates of SS and COD in titanium dioxide wastewater by using PAM modified diatomite to deal with are respectively the1.34times and the1.47times than the removal rates by using raw diatomite. Compared to modified diatomite uesing the methods of activation modification with acid and alkali or roasting, PAM modified diatomite was more effective to deal with titanium dioxide wastewater.By doing orthogonal test, the best preparation conditions for PAM modified diatomite were determined:the dosage of diatomite was50g; the concentration of PAM was40g·L-1; the mixing time was2h; the roasting temperature was750℃; the roasting time was2h. The mechanism of PAM modified diatomite was:the surface activity of diatomite was stimulate by using PAM to modify diatomite, so that the specific surface of diatomite increased, and the negative charge on the surface of diatomite transformed into positive charge.The reasonable processing parameters for using PAM modified diatomite to deal with titanium dioxide acidic wastewater were:using sodium hydroxide to neutralize titanium dioxide acidic wastewater and adjusting pH of the wastewater of about7to8; the adsorption and reaction time was60min; PAM modified diatomite dosage was8g·L-1; at room temperature would be proper reaction temperature. Under these conditions, the removal rates of COD and SS could reach to90%and95%respectively; the organic matter and suspended pollutants in titanium dioxide wastewater had been reduced significantly, and water quality of effluent was clarified; the concentrations of COD and SS were36.8m g·L-1and40.6m g·L-1respectively, which could meet the primary standard of the "Integrated Wastewater Discharge Standard "(GB8978-1996).The experiment of adsorption behavior showed that:(1)The adsorption capacity of diatomite for COD in the titanium dioxide wastewater was far less than the adsorption capacity of PAM modified diatomite for COD. With the increase of the concentration of the solution, the two adsorption capacities gradually increased. And the higher the concentration of the solution was, the difference between two adsorption capacities was more significant.(2)The COD adsorption processing of PAM modified diatomite was exothermic reaction. Low temperature was more conducive to the adsorption reaction.(3)Both Langmuir and Freundlich isotherm models could well describe the discipline of adsorption processing of PAM modified diatomite at constant temperature. The adsorption processing was complex processing of multilayer adsorption, primarily physical adsorption, and chemical adsorption was also included.Correlation coefficient of the Freundlich isotherm fit better than the Langmuir isotherm, which meant that the Freundlich isotherm is more suitable to describe the adsorption processing of PAM modified diatomite for COD in the titanium dioxide wastewater.PAM modified diatomite which could integrate the advantages of PAM flocculant and diatomite flocculation, had good treatment effect when uesed in the treatment of titanium dioxide wastewater. This research provided a new way of thinking for the resource utilization of diatomite and titanium dioxide wastewater treatment processing.