Study On Adsorption-precipitation And Advanced Oxidation For Treating Leaching Tannate Wastewater

Leaching tannate is polynuclear complex formation by reaction of tannic acid and metallic lead ion.It is usually used to be solid propellant of rockets and missiles,and has a good effect in increasing the burning rate and decreasing the pressure index.In the process of producing leaching tannate,a large number of mother liquor and washing wastewater were produced.The wastewater was dark red brown,the color value was as high as 100,the pH value was 5,the COD_Cr value was about 4515.0 mg/L,and the content of Pb²⁺ was about 27.32 mg/L.The wastewater contained refractory organic matter and heavy metals simultaneously,which not only seriously polluted the ecological environment,but also restricted the production of green environmental protection.Therefore,the treatment of leaching tannate wastewater has become an urgent task to be solved..In this paper,three methods,including adsorption,precipitation and advanced oxidation,were used to treat leaching tannate wastewater.The optimum operating parameters were determined and the degradation mechanism was also discussed.Four methods,including precipitation,adsorption,precipitation-adsorption and precipitation-adsorption,were used to treat the wastewate firstly.Through the comparison and analysis of the pretreatment results of various methods,it was found that the best treatment was combination adsorption of D201 resin and precipitation of CaO powder.The removal rate of COD_Cr and Pb²⁺ in thewastewater was 74.4% and 98.2% respectively by D201 resin adsorption;the removal rate of COD_Cr was up to 57.1% after pretreatment with CaO.D201 resin could be regenerated and reused by hydrochloric acid with a concentration of 0.1mol/L and ammonium chloride solution with mass fraction of 15%.Because COD_Cr and chroma of wastewater could not reach the discharge standard after pretreatment by D201 resin and Ca O,it was investigated that photocatalytic oxidation method which was used for advanced treatment in the paper,the optimum reaction conditions for treatment of photocatalytic oxidation: room temperature,pH 7,P25 1.6 g/L,H₂O₂ 6 mL/L.Under the condition,the COD_Cr of wastewater decreased to 87.5 mg/L,the removal rate was 82.3%.The wastewater achieved the discharge requirement of "space propellant water pollution discharge standard"?GB14374-93?.In addition,the wastewater was treated with the Photo-Fenton method in the paper.The optimal process parameters were determined: pH 4.0,H₂O₂ 4 m L/L,n(H₂O₂/Fe²⁺)15.The removal rate of COD_Cr was up to 85%,and the effluent COD_Cr was about 75 mg/L.Finally,the intermediate products of wastewater by Photo-Fenton treatment were analyzed by UV-VIS spectrometer,results showed that tannic acid hydrolysed to gallic acid and glucose,followed by oxidation of alkenes,ketones,aldehydes to carboxylic acids,mineralized to CO₂ and H₂ O at last.