The mechanisms of conventional pollutants adsorption by modified granular steel slag

Abstract

This study was performed to investigate the removal of phosphorus, nitrogen, ammonia and dissolved organic matter (DOM) from domestic wastewater using modified granular steel slag (GSS) as adsorbent. The modification methods include acid modification, alkalinity modification and thermal modification. The GSS modified at 800°C for 1 h was easier to hydrolyze Ca<sup>2+</sup>, which could promote the precipitation of phosphates and the ion exchange process of ammonia. Therefore, the adsorptive capacity of GSS for phosphates and ammonia could be significantly improved by the thermal treatment. The acid-modified GSS promoted the adsorption capacity of nitrates by increasing surface protonation, specific surface area and pore size. The highest nitrates adsorption capacity was obtained when GSS was immersed in 1 mol/L HCl solution for 24 h. The presence of nitrates inhibited the adsorption of phosphates by GSS because the adsorption of nitrates and phosphates by GSS depended largely on electrostatic attraction and intermolecular force, and the competition between them reduced the adsorption capacity. Ammonia can promote the hydrolysis of metal ions on the surface of GSS, increase the concentration of metal ions in solution and promote the formation of phosphate precipitation, but ammonia also competed with phosphate for active sites on the surface of GSS. The effect of ammonia nitrogen on phosphate adsorption was the result of the interaction of the two mechanisms. For domestic wastewater, the thermally modified GSS showed the best adsorption rate of total phosphorus and total nitrogen, and the acid-modified GSS had better adsorption capacity for organic matter. The thermally modified GSS had a good application effect in laboratory subsurface flow constructed wetlands.

Archives of Environmental Protection

“…Interestingly, for all membranes, the retention of N-NO 3 was lower than P-PO 4 retention. It can be explained by competition for adsorption active sites between nitrate nitrogen and phosphate phosphorus [Wang et al 2021].…”

A Review of Modified Steel Slag Application in Catalytic Pyrolysis, Organic Degradation, Electrocatalysis, Photocatalysis, Transesterification and Carbon Capture and Storage

“…When in contact with the acid solution, chemical reactions occur, and soluble salts enter the solution, which changes its structure, increases its specific surface area and pore size, enlarges the contact surface between the steel slag and the reactant, and improves the catalytic performance. However, we should pay attention to the acid concentration during the modification process-too strong an acid solution may lead to a fragile and unstable surface structure of steel slag [23]. Commonly used acid modifiers are hydrochloric acid, sulfuric acid, and some weak acids, such as formic acid and oxalic acid [24][25][26].…”

“…Therefore, the catalytic performance of alkali-modified steel slag in some catalytic applications is better than that of acid modification. Similarly, too high alkaline solution concentration will destroy the pore structure of steel slag, so it is necessary to pay attention to alkali concentration during the modification process [23]. Commonly used alkali modifiers include NaOH and others [28,29].…”