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Adsorption of Boron by Metallurgical Slag and Iron Nanoparticles

Boron is a problematic pollutant because of the difficulty involved in removing it from water with an acceptable cost-to-benefit ratio, especially at extremely high concentrations (600 mg B/l). It is also necessary to remove the pollutant to comply with the quality criteria for drinking water (1 mg B/l) and even for agricultural irrigation purposes (0.5–15 mg B/l depending on crop tolerance). Although some newly proposed water-treatment technologies use economical adsorbents, they are unable to achieve the residual concentrations. The aim of this work is to show that adsorption using metallurgical slags (SL) can be used either as a pre-treatment of the zero-valent iron nanoparticles (nano-Fe0) or as a final treatment itself for removing boron at high concentrations to obtain effluents complying with the standards established for drinking water and wastewater reuse. Adsorption tests (kinetics and isotherms) were carried out for both adsorbents. The slags showed good results as an adsorbent for boron removal in the pre-treatment and final treatment stages, with a very low cost compared with nano-Fe0. The use of slags instead of expensive commercial adsorbents makes adsorption of water with high boron concentrations feasible, and allows obtaining treated wastewater for agricultural irrigation of very tolerant crops.