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A covered mixing tank with mixer is required for the reaction. <br />The auxiliary equipment required consists of aixing tank for <br />the sodium hypochlorite and the sodium hydroxide. <br />The individual shops will have a pretreatment <br />system andthe <br />Facility will require an oxidation react <br />equipment. <br />- . And S1ud4e Thickening <br />Soluble metal salts occur in plating bath dumpnexch <br />thine bath <br />dum;;s, metal finishing rinse tt®sbend the aemovedofrom thegaqueous <br />regenerant solutions. In order <br />solutions the metal salt® must be converted insoluble <br />hydroxides or sulfides. sulfide precipitation This <br />metal from the wastewater than hydrox=emprecipitation. <br />ovete hibulk oof a metal <br />is why a two step process is used to <br />from solution as a hydroxide and then polishing <br />the <br />soluion as <br />with a sulfide precipitation step. Hydr Pr <br />a processt has a greater product flexibility and <br />precipitation. <br />discharge pretreatment requirements t <br />For these reasons hydroxide was chosen as theprecipitator <br />inor <br />the Facility. Metal hydroxide sludges can be <br />redissolvedacids and converted to more soluble formebecauaesof thefor reue. idanger <br />cannot be done with metal sulfide sludges <br />generated. Also. the <br />of toxic hydrogen sulfide gas being ge <br />re uired treatn�nnt of wastewaters from hydroe reemovalio ftexcess <br />q <br />is a simple neutralization with an quire airstripping which is <br />sulfide from the waste <br />much more complicated and expensive. <br />The choice of base to add to the metal solution ution is a imoortan <br />factor affecting both the technical <br />alcium hydroxide and sodium <br />Of <br />the systemCall ium ecommonlyrused. <br />hydroxide are <br />The precipitation of these metalhydroxides equireistn ot ensure an <br />instantaneous so proper equipment <br />adequate retention time for the settlingrmefrom s to metal hydroxide <br />T <br />precipitation must e <br />thickening of the s�lsQebeofacalitated by the equipment. Two <br />standard circular clarifiers with rotating scrapers will be <br />utilized by the Facility. <br />flocculant will most likely be added to the claiferto aid The <br />in a <br />more complete Precipitation of the metalhydroxides. <br />most common flocculants are ferric ohloridea alum and a variety <br />of water soluble polymers. <br />A-7 <br />