Study On Lead And Cadmium Removal From Wastewater By Steel Slag

Adsorption is one of the most widely used methods to eliminate the heavy metal pollutants in water, due to its high removal efficiency and ease of operation. So, to seek an adsorbing material with good adsorption capability and low-cost is the key for adsorption method application. Steel slag, as a kind of solid waste produced in the process of steelmaking, is a suitable adsorbent with large specific surface area and porous structure. Based on these characteristics, steel slag was studied as adsorbent for the removal of lead and cadmium ions sorption from water feature in the study.In this study, the chemical composition of steel slag, properties and structural characteristics were analyzed by using chemical analysis, XRD, BET and SEM. The result showed that the main components of the steel slag were CaO and other metal oxides, which dissolved in the water and led to alkaline of solution; From the result of observation on the steel slag surface, the surface of the steel slag is coarse porous, which is conducive to the adsorption of heavy metal ions in water.By single-ion batch experiments, this paper investigated slag dosage, initial solution pH, reaction temperature and reaction time on the influence of adsorption effect. The results showed that slag dosage and reaction time have a great impact on removal efficiency. The optimal dosing ratios of lead/steel slag was 1:10 and cadmium/slag was 1:20; initial pH and temperature had little effect on the adsorption of heavy metal ions in the slag. So, slag can well adapt to changes in wastewater.Meanwhile, the mechanism of eliminating heavy metal ions by steel slag had also been studied:The observation of the experimental phenomena and characterization of XRD, SEM analysis, showed the process of steel slag to remove lead ion and cadmium ion was the interaction result of chemical precipitation and adsorption. And the Langmuir isotherm models and pseudo-second-order kinetic were more suitable for steel slag adsorption of lead ion and cadmium ion. The adsorption rate of steel slag was controlled by the chemical adsorption mechanism, and its adsorption form was monolayer adsorption.Results of Dynamic adsorption experiments showed that the breakthrough time increased with increasing bed depth, whereas decreased with increasing flow rate, initial metal ions concentration. Dynamic adsorption process was well conform to the Thomas model with R2> 0.9, the operating parameters of the adsorption column can be accurately predicted by using this equation. From the calculation results, the maximum adsorption capacity of lead ion and cadmium ion by adsorption column were 69.86 mg/g and 55.14 mg/g, respectively. The dynamic competing adsorption experiment results showed that the prior adsorption of lead ions and cadmium ions on slag was Pb2+>Cd2+.