| The treatment of high arsenic in natural water and industrial wastewater is considered to be the common challenge worldwide. The concentration of arsenic in Yangzonghai Lake once reached 0.134 mg/L after an accident in June 2008, the water quality becomed inferior Class V from Class II. Our group took measures to govern with FeCl3 as flocculant and coagulant aids, the arsenic concentration of the treated water is basically stable at about 0.05 mg/L, which achieved good treatment effect. In this study, in order to improve arsenic removal efficiency without additional oxygenant, enhanced coagulation-precipitation using FeCl3 as flocculant and sodium bicarbonate, potassium bicarbonate and calcium bicarbonate respectively as coagulant aids were investigated. Further, we also explored various process parameters of novel and efficient flocculation-flotation method of treatment high arsenic industrial wastewater.The follows were the main contents and results of this paper:(1) The coagulant aids exploration of enhanced flocculation-precipitation methodCombined with governance experience of Yangzonghai Lake, NaHCO3, KHCO3 and Ca(HCO3)2 were chose as coagulant aids respectively. The impact of different iron-arsenic molar ratio, pH value for arsenic removal efficiency were investigated. And the advantages and disadvantages of three bicarbonate were compared when they were used as coagulant aids of FeCl3. The results showed that arsenic removal rate was greatly impacted by pH value. Enhanced flocculation-precipitate method can reduce the arsenic concentration under 0.10 mg/L when the iron-arsenic molar ratio was 6.0 with bicarbonate as coagulant aids. In general, the arsenic removal efficiency of Ca(HCO3)2 was superior to NaHCO3 and KHCO3, and the pH of the water less volatile.(2) The research with enhanced flocculation-precipitation method to process high arsenic wastewaterThe concentration of arsenic in the water could be reduced to below 0.05 mg/L, with enhanced flocculation-sedimentation method using Ca(HCO3)2 as coagulant aid and FeCl3 as flocculant to process Hunan mine waste water and simulated groundwater of high arsenic. And with the increase of time, the arsenic concentration of solution would be reduced to less. The possible mechanisms of enhanced flocculation-precipitation in the presence of calcium ions: ①The ferric floc adsorption for calcium ions increased the surface positive charge that promoted the adsorption of arsenic ions;②The netting and co-precipitation of ferric floe;③The calcium ion increased the size of the colloid particles, so that increased the possibility of the separation of the precipitate through the force of gravity.(3)The study on treatment of high arsenic wastewater by flocculation-flotation processIn this paper, the flocculation-flotation method with different surface active agent was used to process high arsenic wastewater. The effects of different conditions of flocculant doses of FeCl3, surfactant concentration, stirring time and interfering ions were investigated by considering the residual arsenic. The results showed that the use of different surfactants resulted in different optimum arsenic removal conditions when with sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS) and sodium oleate as surface active agent. The arsenic removal rate could be improved when adding proper amount of ethanol. At the same time, it was found that the nitrate radical had a constructive role when SDBS as the surfactants. By comparing the three surfactants can be noted that the optimum pH for SDS and SDBS was in the range of 3.5 to 5.5 and for sodium oleate was in the range from 6.5 to 10.5, and the anti-jamming ability of sodium oleate was stronger. |
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