Study On Lead Removal From Acidic Wastewater By Steel Slag

Pb(Ⅱ) acts as pollution source is more and more common, this is a severe threat to the life and health of public.In this article, steel slag was investigated as a absorbent of removing heavy metal Pb(Ⅱ) in aqueous solution.Modern characterization methods (SEM, XRD, BET.ect) were employed to characterize the adsorption samples. The results showed that the chemical composition are mainly CaO,SiO2 and the mineral composition of steel slag are mainly calcium silicate,Ca Fe composite oxide.With a rough and porous surface, steel slag contained various active group like hydroxyl,there was no risk of re-contamination when steel slag was used as water treatment agent.The Box-Behnken design methodology, including four factors:reaction time,particle size of steel slag, initial Pb(Ⅱ) concentration and adsorbent dosage, was employed to study the removal of Pb(Ⅱ) from aqueous solution by steel slag, with the removal of Pb(Ⅱ) as the target response. The best adsorption conditions of Pb(Ⅱ) through response surface analysis method were:reaction time 5h,particle size 80 mesh, initial Pb(Ⅱ) concentration 12.11mg/L, adsorbent dosage 0.77g/L,and the best removal rate of Pb(Ⅱ) was 76.32%.Steel slag was used to remove Pb(Ⅱ) using an upflow-water column. The effects of influencing factors such as particle size of steel slag, bed height, flow rate, height-diameter ratio of bed and lead concentration were studied.The results showed that the breakthrough time would be shortened by increasing particle size, flow rate, height-diameter ratio of bed, lead concentration and decreasing bed height. The maximum absorption capacity of lead was between 32.21-110.45 mg/L, the column efficiency maintained more than 51.15%, indicating that the column exhibited a distinct removal effect on lead ion from aqueous solution. The column adsorption data at different conditions fitted fairly well with BDST model (R2>0.95).The adsorption of Pb(Ⅱ) on the steel slag can be described by langmuir isotherm model、the first-order kinetic model and the intra-particle diffusion model.Thermodynamic adsorption studies showed that the adsorption was a spontaneous process with increased entropy. Composition of filtrate and mineral composition of steel slag were performed to understand the mechanistic steps of the adsorption process.Characterization results showed that ion ecxhange and surface precipitation were the main mechanisms of Pb(Ⅱ) adsorption on the slag.At the end of this paper, taked the wastewater treatment project of lead storage battery factory as an example, compared the reagent cost of traditional chemical precipitation method and steel slag adsorption method. We also compared the maximum adsorption capacity of steel slag, activated carbon and other commonly used adsorbent. The results showed that the reagent cost of steel slag used as wastewater treatment agent was only 0.34 yuan/kg (Pb). Under the same reaction conditions, the theoretical maximum adsorption capacity of steel slag and activated carbon for Pb (Ⅱ) was 130.38mg/g and 221.73 mg/g. In summary, the use of steel slag as Pb (Ⅱ) treatment agent presented significant economic benefits.