Removal Of Heavy Metal Chromium And Nickel From Pickling Waste Liquor

In recent years,there have been many implementations of the resource utilization of pickling waste liquid,such as crystallization of ferrous chloride,roasting iron oxide powder,chemical conversion water treatment agent,etc.,but no acid washing was considered in these application projects.The problem of purification of heavy metals in waste liquids.In this paper,the purification method of heavy metals in pickling waste liquid was studied,and the feasibility of iron powder reduction method and phosphate method for removing heavy metals in pickling waste liquid was explored.Through orthogonal test,single factor analysis and precipitation characterization analysis,the optimal reaction conditions were determined,the reaction mechanism was explored,and the actual pickling waste was verified.1.The iron powder reduction method had a better removal effect on chromium(the chromium in the paper refers to trivalent chromium unless otherwise stated)and nickel.The main factors influencing the effect of iron powder reduction on chromium removal are initial pH.The secondary factors are iron powder dosage,then reaction time and reaction temperature.The optimal combination scheme is: initial pH 0.4,iron powder dosage 20 g/L,temperature 40 °C,reaction time 1.5 hours,under this scheme,the chromium removal rate was 88.5%.The main mechanism of chromium removal was coprecipitation and adsorption of iron powder and hydroxide;The main influencing factor for nickel removal is the reaction temperature.The secondary factor was the iron powder dosage,followed by the initial pH and reaction time.The optimal combination scheme was: temperature 80 °C,iron powder dosage 60 g/L,reaction time 3 h,pH value 0.5,under this scheme,nickel removal rate is 92.9%.The main mechanism of nickel removal was displacement,iron powder and iron oxide adsorption.2.The phosphate precipitation method had a good effect of removing chromium,but the iron loss rate was high,and the removal effect of nickel was poor.The order of the factors influencing the removal of chromium was: initial pH > sodium phosphatedosage > reaction time > reaction temperature,the optimal reaction conditions were initial pH 0.4,sodium phosphate dosage is 20 /L,temperature 40 °C The reaction time was 30 minutes.Under this condition,the removal rate of chromium was 78.5%,and the iron loss rate was 26.9%.The main mechanism of chromium removal was the formation of chromium phosphate precipitates and the formation of iron-chromium ferrite precipitates,as well as the adsorption of FeOOH;The primary and secondary order of each influencing factor when removing nickel was: sodium phosphate dosage > initial pH > reaction temperature > reaction time.The optimum reaction conditions were sodium phosphate dosage of 60 g/L,initial pH value 1,reaction time of 2 hours,and temperature of 30 °C.Under this condition,the nickel removal rate was 15.6%,and the iron loss rate was 46.7%.In addition to the mechanism of nickel,the adsorption of nickel and phosphate forms precipitated iron hydroxide.3.The removal effect of chromium by the combination of phosphate and iron powder method was better than that of the two methods alone,and the order of the influencing factors also changed: pH>reaction time>phosphate iron powder dosage ratio>temperature.The optimal reaction conditions had lower initial pH and faster reaction rate,specifically: initial pH 0.1,reaction time 15 min,phosphate dosage 50g/L,iron powder dosage 20 g/L,reaction temperature 25 °C.Under this condition,the chromium removal rate was 91.9%,and the iron loss rate was 3.5%,which was 13.4%higher than the chromium removal rate alone,and the iron loss rate was decreased by23.4%.The presence of chromium after removal was dominated by the adsorption state of chromium phosphate,ferrochrome precipitate and iron hydroxide;the removal effect of nickel by phosphate combined with iron powder method was general,and the removal rate was between iron powder method and phosphate method.4.The above three methods were verified in the actual waste acid.The removal effect of chromium and nickel was slightly lower than that in the simulated pickling waste liquid.The main reason was that there were many coexisting heavy metal ions in the actual pickling waste liquid influences.The effects of other heavy metal ions on the removal of chromium and nickel from pickling waste liquid by iron powderreduction method were investigated.The results showed that nickel can promote the removal of chromium when chromium-nickel coexists,but the removal of nickel by nickel was inhibited.The role of lead and copper will inhibit the removal of chromium,lead also inhibits nickel,copper has little effect on the removal of nickel.