| Aluminum is a kind of environmental protection material with the feature of energy saving, more and more aluminum products widely used in construction, packaging, transportation and other industries. The treatment of aluminum surface is a indispensable process to manufacture aluminum product, which will consume a mass of water, generate a large amount of wastewater with complicated chemical composition, contains masses of Al3+, SO42-, Cr6+ Cr3+, F-, PO43-, etc. If not treated, it would pollute the environment seriously.A factory's aluminum surface treating liquid was taken as water sample in article, remove the Cr6+, F-, PO43-, SO42-,Al3+ of wastewater step by step:Cr6+ removed by ferrite method; F-, PO43- and SO42- removed by coagulation-chemical precipitation method; Al3+ removed by crystallization method. The purpose of the study is to explore the removal effect of various kinds of ions which influenced by adding concentration and reaction conditions. The results of experimental show that the effect of experimental influenced by the factors such as adding concentration, the value of pH, reaction temperature, reaction time, stirring speed greatly. It mainly shows in:(1) In the experiment of removing Cr6+ in wastewater by ferrite method, the optimum process conditions are:the adding concentration of FeSO4·7H2O is 56g/L, the value of pH during redoxomorphic stage is 4, the value of pH during coprecipitation stage is 9, the temperature is 75?, the stirring time is 20min. Under the optimum process conditions, the removal rate of Cr6+ reaches to 99.98%, the concentration reduced from 1539 mg/L to 0.29 mg/L, below the discharge standard of chromium-containing wastewater 0.5mg/L.(2) In the experiment of removing F-, PO43- and SO42- in wastewater by coagulation-chemical precipitation method, the optimum process conditions are:the adding concentration of CaO is 23g/L, the adding concentration of PAC is 2.2 g/L, the adding concentration of PAM is 1.7 g/L, the value of pH is 9, the reaction time is 30min, the reaction temperature is 50?. Under the optimum process conditions, the removal rate of F- reaches to 99.94%, the concentration reduced from 7658 mg/L to 4.30 mg/L, below discharge standard of fluoride-containing industrial wastewater of 10 mg/L; the removal rate of PO43- reaches to 95.90%, the concentration reduced from 22 mg/L to 0.90 mg/L, below the grade ? discharge standard of phosphate-containing industrial wastewater of 1.0mg/L; the removal rate of SO42-reaches to 98.58%, the concentration reduced from 8773 mg/L to 125 mg/L, below the maximum permissible sulfate concentration in drinking water standard of 250mg/L.(3) In the experiment of removing Al3+ in wastewater by crystallization method, the optimum process conditions are:the adding concentration of (NH4)2SO4 is 3.84g/L, the value of pH is 9, the temperature is 25?, the reaction time is 6h, the stirring speed is 40r/min. Under the optimum process conditions, the removal rate of Al3+ reaches to 99.97%, the concentration reduced from 525 mg/L to 0.14 mg/L, below the maximum permissible concentration of Al3+ in drinking water standard of 0.2 mg/L.(4) As show as the resullts of comprehensive experiment,the appliment of optimum process conditions to water samples in separate experiment will lead to the effects as follows:the removal rate of Cr6+ reaches to 99.99%, and the residual concentration is 0.19mg/L; the removal rate of F- reaches to 99.91%, and the residual concentration is 6.61 mg/L; the removal rate of PO43- reaches to 96.32%, and the residual concentration is 0.81mg/L; the removal rate of SO42- reaches to 98.06%, and the residual concentration is 170.45mg/L; the removal rate of Al3+ reaches to 99.97%, and the residual concentration is 0.17mg/L. Eventually, Cr6+, F-, PO43-, SO42-, Al3+ in the wastewater, are all reach discharge standards. |
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