Study On The Wastewater Containing Zinc Iron And Cyanide From Iron And Steel Industry By Chemical Treatment

Some treatment methods in recent years for the wastewater containing zinc and cyanideare described in detail in this paper. There are many methods of processing the wastewater,but how to choose the method is based on the source and composition of wastewater, thepurpose and the scale of the process.This paper uses three kinds of single process: sodium hypochlorite-hydroxideprecipitation, chlorine dioxide-hydroxide precipitation, ferrous sulfate-hydroxide precipitationand the combined process of ferrous sulfate-sodium hypochlorite-hydroxide precipitation tostudy containing zinc and cyanide washing wastewater of blast furnace gas. The optimumtechnical conditions for single process experiment are obtained by the orthogonal test andinfluencing factors experiment. The optimum technical conditions which get from singleprocess experiment was used in the combined process experiment for wastewater treatment,after treatment, the concentration of total cyanide and zinc ion are0.43mg/L and0mg/Lrespectively in wastewater.Sodium hypochlorite-hydroxide precipitation has a good removal result for thewastewater containing zinc iron and cyanide from iron and steel industry. In the conditions ofthe orthogonal experiment, the results of removal zinc and cyanide can be reproducible. Theoptimum technical conditions are obtained by the orthogonal test and influencing factorsexperiment as follows: pH is in a range of9~10; the temperature is25℃; content of effectivechlorine is250mg/L and stirring time is30minutes. After treatment, the total cyanideconcentration in wastewater is0.39mg/L; the removal rate of total cyanide and zinc ion are99.12%and100%respectively, which can reach the national level of dischargingstandard(GB8978—1996).In the conditions of the orthogonal experiment, the chlorine dioxide-hydroxideprecipitation has reproducible results of removal zinc and cyanide. The optimum technicalconditions are obtained by the orthogonal test and influencing factors experiment as follows:pH is in a range of9~10; the temperature is30℃; content of effective chlorine is600mg/Land stirring time is30minutes. After treatment, the total cyanide concentration in wastewateris0.47mg/L; the removal rate of total cyanide and zinc ion are99.74%and100%respectively,which can meet the national level of emission standard(GB8978—1996).Ferrous sulfate-hydroxide precipitation has a good removal result for the wastewater containing zinc iron and cyanide from iron and steel industry, but the effluent water can’tmeet the national discharge standard. In the conditions of the orthogonal experiment, theresults of removal zinc and cyanide can be reproducible. The optimum technical conditionsare obtained by the orthogonal test and influencing factors experiment as follows: pH is6; thetemperature is30℃; ferrous sulfate dosage is3.5times as the theoretical and stirring time is30minutes. After treatment, the concentration of zinc ion and total cyanide are0mg/L and2.60mg/L respectively in wastewater.Ferrous sulfate-sodium hypochlorite-hydroxide precipitation allows the wastewater toachieve the national emission standards. The optimum technical conditions as follows: pH is6;the temperature is30℃, ferrous sulfate dosage is3.5times as the theoretical and stirring timeis30minutes; and then continue to add the content of effective chlorine is100mg/L sodiumhypochlorite to the wastewater, stirring time is30minutes. After treatment, the total cyanideconcentration in wastewater is0.43mg/L, the removal rate of total cyanide and zinc iron are99.03%and100%respectively. In the raw water pH conditions, other technical conditionsunchanged, when the content of effective chlorine is167mg/L, the effluent water can achievethe first class discharging standard of our country(GB8978—1996).Through the practical application of sodium hypochlorite-hydroxide precipitation andferrous sulfate-sodium hypochlorite-hydroxide precipitation at the production site for sometime, detected the mean concentration of total cyanide are4.42mg/L and3.85mg/Lrespectively, zinc ions are14.71mg/L and13.22mg/L respectively in the water samples of oneabsorbent well, which can meet the internal standards of Xiangtan iron and steel groupcompany limited for industrial recycling water.(Q/OHAB801.1-2009)(total cyanide≤10mg/L,zinc ions≤30mg/L)...