Removal efficiency of arsenic in water using desulfurization slag

Abstract

AbstractThe steel industry in Taiwan produces more than 3 million tons of steelmaking slag per year on average. Conventional solidification and landfilling methods are no longer suitable for the highly populated small island as a wide area is needed for such methods. This study aims to improve the quality of polluted water bodies using desulfurization slag – a recycled product resulted from steelmaking – as an arsenate adsorbent. Experimental results revealed that desulfurization slag pH and metal ions including Ca, Mg, Fe, and Mn affected the behavior and content of arsenate existing in an aqueous solution. The concentration of Ca among these metal ions is the highest in the aqueous solution, which facilitates the formation of calcium hydroxyarsenate and is therefore more critically beneficial than other metal ions in removing As in the aqueous solution. Additionally, desulfurization slag samples with particle size of >200 mesh had a greater specific surface area compared to those in other particle sizes, suggesting preferable As adsorption ability of slag with higher mesh numbers. Such desulfurization slag samples were thus used in subsequent adsorption experiments in this study. The energy dispersive spectrometry results confirmed that the >200‐mesh group comprised the highest metal oxide content in terms of As removal. This study found that under different Cl− and SO42− concentrations, the covalent bond effect did not significantly affect the slag's ability to adsorb As. According to the adsorption isotherm experiment results, the Langmuir model (R2 = 0.998) outperformed the Freundlich model (R2 = 0.961) possibly because the former is suitable for situations with even energy distribution and monolayer adsorption, while the latter is often applied to scenarios with uneven distribution and multilayer adsorption, indicating that the adopted desulfurization slag adsorbed arsenate through the mechanism of monolayer adsorption. There are many useful contents in the desulfurization slag. In terms of sustainable use of resources, desulfurization slag is worthy of economic development and reusing if recycled. Currently, there is little research and information on desulfurization slag in Taiwan. Hopefully, this study will be helpful for future development and application of desulfurization slag in recycling techniques.