Removal Of Cyanide And Thiocyanide From Cyanide Tailings Washing Solution

Cyanide tailings come from the gold ore extraction smelting process,which have the characteristics of high yield and toxicity.Cyanide tailings are extremely harmful to human health and ecological environment.The treatment of cyanide tailings is a common problem that all gold smelters have to face.The cyanide tailings can meet the standard of entering the tailing pond after being treated by the pressure filter washing process.And the purification of cyanide tailings can be transformed into the treatment of cyanide tailings washing solution.In this paper,the treatment methods of washing solution was studied with the simulated solution and the washing solution of cyanide tailings as raw materials,hoping to help the treatment of industrial cyanide wastewater such as cyanide tailings washing solution.Ferrous salts were used to remove cyanide from the washing solution.The effects of reagent addition,reaction pH and reaction time on cyanide precipitation were investigated.The optimal reaction conditions were as follows:FeSO4·7H2O dosage was 3.512 g·L-1,which was 2.0 times of the theoretical reagent dosage.The reaction pH value was 5.00-6.00 and reaction time was 30 min.The total cyanide concentration in washing liquid can be reduced to less than 50 mg·L-1,which met the requirements of repeated use in washing cyanide tailings.The Prussian blue precipitation is extremely unstable under strong alkaline conditions and decomposes into ferricyanide or ferrocyanide.Investigated the effects of reagent addition,reaction pH and reaction time on the removal of thiocyanide by copper salt precipitation method.The optimal reaction conditions were as follows:CuSO4·5H2O dosage was 5.111 g-L-1,which was 1.0 times of the theoretical reagent dosage.Na2S2O5 dosage was 1.457 g·L-1,which was 1.5 times of the theoretical reagent dosage.The reaction pH value was 4.00～5.00 and reaction time was 30 min.The removal rate of SCNwas over 95%in washing liquid.Since the precipitation reaction rate of SCN’ was very fast,the reaction pH and reaction time had little effect on reaction.The reaction product was mainly CuSCN precipitation.Copper powder was used as reducing agent to modified copper salt precipitation method.The effects of reagent addition,stirring rate,reaction pH and reaction time on thiocyanide precipitation were investigated.The optimal reaction conditions were as follows:CuSO4·5H2O dosage was 2.771 g·L-1,which was 1.0 times of the theoretical reagent dosage.The copper powder dosage was 3.547 g·L-1.The reaction pH value was 3.00～4.00 and reaction time was 30 min.The removal rate of SCN-was over 88%in washing liquid.Increasing the stirring rate can increase liquid-solid contact area and promote the reduction of Cu2+.As a reducing agent,copper powder was more stable and did not introduce soluble ions or generate additional consumption.Under strong acidic conditions,the addition of excessive copper powder was beneficial to increase the reaction rate.The reaction products were mainly CuSCN,Cu2O and residual copper powder.Investigated the effects of catalyst types and concentration,H2O2 addition,reaction pH and reaction temperature on the removal of thiocyanide by hydrogen peroxide oxidation method.The optimal reaction conditions were as follows:Fe2+catalyst dosage was 3.0 g·L-1,30%of H2O2 solution dosage was 10.125 ml·L-1,which was 1.0 times of the theoretical reagent dosage.The reaction pH value was 2.00-3.00 and reaction time was 30 min.The removal rate of SCNwas over 85%in washing liquid.The oxidation reaction rate of SCN-was greatly affected by reaction temperature and the catalyst concentration.The reaction pH affected the oxidation reaction rate of SCN-by influencing the catalyst concentration in solution.In the Fenton or Fenton-like system,SCN-can be completely oxidized to SO42-and CN-.While CN-was partially oxidized,the element C was oxidized to CO32-and element N was oxidized to NH4+and NO3-.Some CN-reacted with Fe3+or Fe2+in solution,and only a very small amount of CN-escaped as HCN under strongly acidic conditions.When reaction pH value was 2.00-3.00 and reaction temperature was about 20℃,the apparent kinetic equation of H2O2 and SCN-oxidation reaction was:r=2.077×10-5cSCN-1.329 cH2O20.714 cFe3+1.174.