Experimental Study On Construction Of Advanced Reduction System And Removal Of Cr(?)from Wastewater Based On Activated Carbon

Hexavalent chromium mainly comes from waste water discharged from mining,tanning,cement,iron,steel and other metal alloy production and electroplating.At present,the treatment of hexavalent chromium wastewater is divided into two main categories.in the detoxification of Cr???,the critical process is reduction of the Cr???to Cr?III?,such as chemical reduction,electrochemical method,photochemical method and bioremediation method,and other methods are to remove Cr???by adsorption and flocculation.Chemical reduction has been widely concerned because of its good effect and rapid reaction.However,the disadvantage is the low utilization rate of reductant.Activated carbon is cheap and easy to obtain,it has become a very common adsorbent for its convenient operation,but the removal process is long and the removal efficiency is low.Therefore,it is of great significance to study cheap and efficient methods for the remediation of hexavalent chromium pollution in water.Based on the new and developing carbon dioxide ion free radical,a new and efficient reductant,the adsorption and activation properties of activated carbon were studied.In this paper,hexavalent chromium in water was used as the target pollutant and activated carbon as adsorbent and activator.Using persulfate and formate as reaction reagents,the recovery technology of hexavalent chromium in water by adsorption and reduction was established.The ability of activated persulfate/formate system to remove hexavalent chromium in water was studied experimentally.Three kinds of activated carbon materials are:acid pickling activated carbon?HCl-AC?,nano-activated carbon?NAC?and magnetic nano-activated carbon?NAC-Fe₃O₄?.The results show that:?1?HCl-AC/PS/FA system has a good effect on the removal of hexavalent chromium in water.The removal mechanism of hexavalent chromium in water is divided into two parts.One is the adsorption of hexavalent chromium by HCl-AC.The adsorption of hexavalent chromium onto hexavalent chromium is in accordance with the Fruendlich isothermal adsorption model.The quasi-second-order kinetic model shows that the adsorption chemisorption of hexavalent chromium by HCl-AC is dominant.Second,HCl-AC activates persulfate to produce sulfate radical,then reacts with formate to form carbon dioxide ion radical.The hexavalent chromium is reduced to trivalent chromium.In addition,HCl-AC also adsorbs trivalent chromium from solution and the hexavalent chromium adsorbed on HCl-AC.The removal mechanism of HCl-AC/PS/FA/PSFA system is the same as that of HCl-AC/PS/FA system.The reduction of hexavalent chromium in NAC/PS/FA system is dominant,and the reduction rate is above 73%.NAC-Fe ₃O ₄/PS/FA system has a good effect on the removal of hexavalent chromium in water.The mechanism of reduction of hexavalent chromium in water is more complex than that of the former two systems.The divalent and trivalent iron ions also participate in the reaction.?2?for six valent chromium with initial concentration of 50 mg/L,HCl-AC of 2g/L,NAC of 1 g/L,1.5 g/L NAC-Fe₃O₄ is the most suitable dosage of three kinds of activated carbon.When 10 mm PS and 10 mm FA are added in the system,the hexavalent chromium in the solution can almost be removed.The higher the amount of activated carbon is,the better the removal effect is.Hexavalent chromium can be completely removed when FA/PS is greater than or equal to 1,and the lower the initial pH is,the better the removal of hexavalent chromium is.?3?among the three activated carbon,HCl-AC has the lowest cost,the adsorption efficiency is the highest,and the particle size is easy to filter out,but the reduction efficiency of NAC in the system is moderate and the reduction efficiency is the highest in the NAC/PS/FA system.However,because of its small particle size,the cost of solid-liquid separation is increased.NAC-Fe ₃O ₄ has the highest production cost and moderate treatment effect,but it is convenient for solid-liquid separation and material recycling.The three kinds of activated carbon have certain significance for the construction of advanced reduction system and the efficiency of Cr???polluted water treatment.