Boron Adsorption-Desorption by Steelmaking Slag for Boron Removal from Irrigation Waters
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Boron Adsorption-Desorption by Steelmaking Slag for Boron Removal from Irrigation Waters Athanasios Balidakis & Theodora Matsi
Received: 26 March 2020 / Accepted: 13 July 2020 # Springer Nature Switzerland AG 2020
Abstract Steelmaking slag, a by-product of the steelrefining process, could be used for removing boron excess from irrigation natural and waste waters, due to its strongly alkaline reaction. The objectives of this study were to: (a) establish the optimum conditions (external solution/adsorbent ratio, equilibration time) of boron adsorption by the slag, (b) assess the slag’s capacity to adsorb boron, and (c) study boron desorption from the slag with time. Boron adsorption increased with the increase of the external solution/adsorbent ratio up to the ratio of 200:1. Although, almost 40% of boron was adsorbed within the first hour of equilibration period, the adsorption gradually increased until the 72 h. The Langmuir adsorption maximum for boron was 145 mg g−1, considerably higher than other adsorbents, like fly ash, calcite, and magnesia. At boron initial concentrations lower than 6 mg L−1, slag removed 55% of boron and reduced it below the permissible levels for irrigation waters (< 4 mg L−1) for most crops. The pH of the equilibrium solution was 10.3 ± 0.8 and dropped to acceptable levels for irrigation waters (< 8.5), after contact with atmosphere for 1 week. Almost 25% of boron was released from samples of boron-laden slag during the first hour of desorption. Consequently, steelmaking slag can be used effectively for removing boron excess from irrigation waters. However, attention should be given to the pH of the slag-treated waters. A. Balidakis : T. Matsi (*) Soil Science Laboratory, Faculty of Agriculture, Aristotle University of Thessaloniki, 54124 Thessaloniki, Greece e-mail: [email protected]
Furthermore, the disposal of boron-laden slag to soils should be practiced with caution to avoid possible boron phytotoxicity risk. Keywords Adsorption . Boron . Irrigation waters . Steelmaking slag
1 Introduction Irrigation waters are one of several sources contributing to high soil boron levels, which could result in boron phytotoxicity (Chauhan and Powar 1978). Boron sources in irrigation waters are usually natural minerals, industrial, urban, and agricultural wastes (Gupta 1993; Waggott 1969). According to Ayers and Westcot (1985), irrigation with waters containing boron concentration higher than 4 mg L−1 can cause adverse effects on most crops (sensitive and moderately tolerant) and increase soil available boron (commonly estimated by the hot water extractable boron) at undesirable levels. Soil boron toxicity levels for crops (i.e., hot water extractable boron > 5 mg kg−1) are very close to the sufficiency levels (i.e., hot water extractable boron 0.5–1 mg kg−1); closer than those of any other essential nutrient for plants (Johnson and Fixen 1990). Consequently, the soil boron status can easily change from sufficiency or even deficiency to toxicity, under false agricultural practices. Therefore,
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