| The mainstream vanadium industrial wastewater is a typical acidic heavy metal wastewater with high concentration and high toxicity.The main pollutants in the wastewater are hexavalent chromium(Cr(?)),total chromium(TCr),vanadium(?)and ammonia nitrogen(NH3-N).Electroplating wastewater is also a common chromium-containing wastewater,the main pollutants in the wastewater are hexavalent chromium(Cr(?))and total chromium(TCr).This kind of wastewater poses a serious threat to human and environmental health.In this papaer,a novel treatment for vanadium industrial wastewater and electroplating chromium-containing wastewater using a byproduct of flue gas desulfurization(FGD)is explored.This study not only provides a low cost and efficient treatment technology for the vanadium industrial wastewater and electroplating wastewater,but also provides a new resource utilization method of the flue gas desulfurization by-product.Compared to traditional methods,the new technology achieves the excellent objective of "waste control by waste",which completely accords with the requirements of green and sustainable development.In this paper,the main components of wet magnesia FGD byproduct from Shandong Binzhou and Datang Lubei thermal Power Plant,and the main components of semi-dry calcia FGD ash from a sintering plant in Hebei province are investigated,respectively.The main pollutants composition and existing forms in vanadium industrial wastewater from a vanadium plant in Chengde,and the main pollutants composition and existing forms in the electroplating wastewater from a electroplating plant of civil aircraf company in Shenyang were investigated.The corresponding treatment processes were designed according to the characteristics of the FGD byproducts from different sources,respectively.The main mechanism,influencing factors,precipitate composition and morphology of the water treatment technology were investigated.The wet magnesia FGD byproduct from Shandong Binzhou Power Plant was used to treat vanadium industrial wastewater,and the heavy metals and ammonium in the wastewater could be precipitated respectively.In the process,the byproduct can be used as reductants to reduce Cr(?)and V(?)to Cr(?)and V(?)which are less toxic and easy to separate,the byproduct can also be used as ammonium precipitators and raw materials for chromium magnesium spinel precursors.The optimum conditions are as follows:in the stage of Cr(?)and V(?)reduction,the optimum pH=2.5,the byproduct dosage is 21.5 g/L,reaction time is 15.0 min;in the stage of TCr and V precipitation,the optimum pH=7.0,the reaction time is 15.0 min;in the stage of ammonium precipitation,the optimum pH=9.5,the molar ratio n(Mg2+):n(NH4+):n(PO43-)=0.7:1.0:1.0,the reaction time is 15.0 min.Under the optimal conditions,the residual concentrations of hexavalent chromium,total chromium and vanadium are 0.046 mg/L,0.468 mg/L and 0.06 mg/L,respectively.The removal efficiency of ammonium is 95.72%and the residual concentrations of ammonium and phosphorus are 137.12 mg/L and 5.49 mg/L,respectively.The heavy metal precipitation can be used to product magnesium chromium spinel(MgCr2O4)by roasting at 1000?,and the main composition of ammonium precipitation is struvite(MgNH4PO4·6H2O)which can be used as controlled release fertilizer.The wet magnesia FGD byproduct from Datang Lubei Power Plant was used to treat vanadium industrial wastewater,and the heavy metals and ammonium in the wastewater could be simultaneously removed.The optimum conditions are as follows:in the stage of Cr(?)and V(?)reduction,the optimum pH=2.5,byproduct dosage is 42.5 g/L,the reaction time is 15.0 min;in the precipitation stage,the optimum pH=9.5,the molar ratio n(Mg2+):n(NH4+):n(PO43-)=0.3:1.0:1.0,the reaction time is 20.0 min.Under the optimal conditions,the residual concentrations of hexavalent chromium,total chromium and vanadium are 0.047 mg/L,0.1 mg/L and 0.14 mg/L,respectively.The removal efficiency of ammonium is 94.5%and the residual concentrations of ammonium and phosphorus are 176.2mg/L and 14.7 mg/L,respectively.The main components of precipitation are struvite and chromium hydroxide mixture.The semi-dry calcia FGD ash from a sintering plants in Hebei was used to treat vanadium industrial wastewater,and the gypsum,heavy metals and ammonium in the wastewater could be precipitated,respectively.In the progress,the semi-dry calcia FGD ash can be used as reductants to reduce Cr(?)and V(?)to Cr(?)and V(?)which are less toxic and easy to separate,and the byproduct gypsum is also obtained.The optimum conditions are as follows:in the stage of Cr(?)and V(?)reduction,the optimum pH=2.5,byproduct dosage is 29.5 g/L,reaction time 15.0 min;in the stage of TCr and V precipitation,the optimum pH=7.5,the reaction time is 15.0 min;in the stage of ammonium precipitation,the optimum pH=9.5,the molar ratio n(Mg2+):n(NH4+):n(PO43-)=1.1:1.0:1.0,the reaction time is 15.0 min.Under the optimal conditions,the residual concentrations of hexavalent chromium,total chromium and vanadium are 0.163 mg/L,0.395 mg/L and 0.155 mg/L,respectively.The removal efficiency of ammonium is 95.75%and the residual concentrations of ammonium and phosphorus are 133.6 mg/L and 5.61 mg/L,respectively.The main component of reduction stage precipitate is gypsum(CaSO4·2H2O),the heavy metal precipitation can be used to product chromium oxide(?Cr2O3=83.72 wt%)powder by roasting at 1000?,the main component of ammonium precipitation is struvite.The wet magnesia FGD byproduct from Shandong Binzhou Power Plant was used to treat the electroplating chromium-containing wastewater,and the byproduct could be used as a low-cost reductant to reduce Cr(?)to Cr(?)which are less toxic and easy to separate.The optimum conditions are as follows:in the stage of Cr(?)reduction,the optimum pH=2.5,byproduct dosage is 0.55 g/L,reaction time 15.0 min;in the stage of TCr precipitation,the optimum pH=7.5,the reaction time is 15.0 min.Under the optimal conditions,the residual concentrations of hexavalent chromium and total chromium are 0.035 mg/L and 0.08 mg/L,respectively.The semi-dry calcia FGD ash from a sintering plants in Hebei was used as a low-cost reductant to treat the electroplating chromium-containing wastewater.The optimum conditions are as follows:in the stage of Cr(?)reduction,the optimum pH=2.5,byproduct dosage is 0.65 g/L,reaction time 15.0 min;in the stage of TCr precipitation,the optimum pH=7.5,the reaction time is 15.0 min.Under the optimal conditions,the residual concentrations of hexavalent chromium and total chromium are 0.021 mg/L and 0.08 mg/L,respectively. |
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