Treatment Of High Fluoride-containing Acidic Industrial Wastewater By Preoxidation-chemical Coagulation Precipitation-adsorption Method

With the development of modern industry, the increasing discharge offluoride-containing industrial wastewater seriously threatens the environment and humanbeings. The high equipment cost, high running fee and unstable remove results are themain disadvantages of the usually used fluoride removal techniques. In the present case,there is an urgent demand for a chemical plant in Jiangsu province to treat thehigh-concentration fluoride containing acidic waste water. The combined technique ofperoxidation-chemical coagulation precipitation-adsorption was designed to insure thewater fluoride in discharged waste meet the National discharge limitation. The main workwas described as follows：The fluoride removal effect from wastewater model of the coagulants polymericferric sulfate (PFS) and polyaluminium chloride (PAC) were compared, the resultsindicated that: the fluoride removal rate of PAC was better than PFS. Under the sameconditions, using PAC coagulant can not nolylead to the lower concentration of residualfluorine, but also acceleratethe settlement process. The conditions, such as the precipitantdosage CaCl2, pH, coagulant dosage, and the coexistence anion play important roles onfluoride removal.The fluoride removal effect of homemade chlorine magnesium aluminumhydrotalcite (Cl-LDH), montmorillonite-PAC and diatomaceous earth-PAC werecompared, which showed that: Cl-LDH was superior than either montmorillonite-PAC ordiatomaceous earth-PAC on fluoride removal. The F-adsorption capacity ofmontmorillonite or diatomaceous was very low, when PAC coagulant was added,enhancing the effect of fluoride removal. With an initial F-concentration of15mg/L, withboth montmorillonite and diatomaceous dose of1g/L，PAC dose of400mg/L，60%and72%of fluoride were transferred to montmorillonite-PAC diatomaceous earth-PAC,respectively. While to the Cl-LDH, with initial F-concentration of40mg/L, with Cl-LDHdose of1g/L，fluoride removal rate was92%.The COD removal effect from actual wastewater of fenton oxidation, aerationtreatment and NaClO oxidation were compared. We found fenton oxidation effect is thebest. For the high COD value (3033.9mg/L) of the actual industry wastewater, with the H2O2dose of10mL/L, H2O2/Fe2+molar ratio of15:1, and oxidation time of1h, CODremoval efficiency reached71.5%.For acidic actual wastewater, we used Ca(OH)2and CaCl2as joint precipitant，PACas coagulant，CPAM as coagulant-aid. Which showed that: with the Ca(OH)2dose of7g/L,CaCl2dose of22.5g/L, PAC dose of600mg/L, CPAM dose of15mg/L, and precipitationtime of30min, the moisture content of precipitation was52.17%，effluent concentration ofF-from initial6200mg/L reduced to about22mg/L.The results of Cl-LDH adsorption treatment of actual wastewater show that: with theCl-LDH dose of3g/L, and contact time of1h, a small amount of400mg/L PAC and4mg/LCPAM, could facilitate the separation of the precipitate which lead to the fluoride removalrate of90%, the effluent concentration of F-reduced to2.49mg/L from the initialconcentration of25mg/L, which meet the national discharge limits.The capacity of fluoride removal suggests that the combined process ofpreoxidation-chemical coagulation precipitation-adsorption technique has a potential tooffer great performance on high fluoride containing acidic wastewater with high CODvalue in real industry wastewater treatment.