Study On The Treatment Of Kaolin Acid Waste Water And Decalcification Of Treated Wastewater

There are many acidic waste water produced and high quality water space in thekaolin production process. If reusing the treated acidic wastewater, it can reduce theenvironmental pollution and reduce the production cost. This study was aimed to treatthe kaolin mineral processing wastewater after neutralization by lime and decalcifyingby "induced crystallization-flocculation precipitation" new process for the optimalprocess parameters. CaCO3and CaSO4coprecipitation process was also studied. Theresults are as follows:1. CaCO3and CaSO4coprecipitation process:(1) The balance of the calcium ionconcentration increased with the increase of sulfuric acid root ion concentration. Whensulfuric acid root ion concentration reached50%~80%, the effect was close to flat.(2)The balance of calcium ion and sulfate ion concentration were decreased with theincrease of temperature. That is c(Ca2+)60℃＞c(Ca2+)70℃＞c(Ca2+)80℃,c(SO42-)60℃＞c(SO42-)70℃＞c(SO42-)80℃.(3) The solubility product of calcium sulphate wasreduced in the different solution with the increase of temperature. With the increase ofproportion of sulfuric acid root ion, the solubility product of calcium sulphate alsoincreased. The solubility product of single sediment has not adapted to thecoprecipitation process.(4) By the scanning electron microscopy (SEM),the calciumcarbonate precipitation crystal was white powder and the calcium sulfateprecipitation crystal was transparent acicular. It was impossibility to see thetransparent acicular crystal in the mixed solution. The calcium carbonateprecipitation crystal was hexagonal structure and the calcium sulfate precipitationcrystal was the needle shape structure. Hexagonal crystals growed on the needlecrystal shape when mixed.2. Kaolin acidic waste water was treated by neutralization and decalcification:(1)The Optimum reaction conditions of neutralization by lime were: The pH controlledbetween9~12; the mixing time was15min; the precipitation time was20min.(2)The wastewater treated by "induced crystallization-flocculation precipitation" newprocess did not scale.(3)In the induced crystallization process, the single factorexperimental results showed that the optimal mixing temperature was50℃,the bestmixing time was40min, the optimal additive quantity of the seed is1mg/L, theoptimal pH value was8.8, the best stirring speed was150r/min. The results of theorthogonal experiment were: the mixing temperature was60℃, the mixing time was 40min, the pH value of8.8. The decalcification rate on average was51.26%underthe optimum condition. The induced crystallization process can be described throughthe crystal growth dynamics model and the related coefficient was greater than0.98.(4) In the flocculation precipitation process, the optimum technological conditionswere: The dosage of PAM was1mg/L; the slow stirring speed was50r/min; the slowmixing time was8min and the settling time was30min. The coprecipitationphenomenon between the calcium carbonate and the calcium sulfate was furtherconfirmed through SEM analysis.