Innovative Process for Extracting Active Silicon From Iron and Steel Slag to Utilize as Fertilizer

by Nattawadee Wisitruangsakul

Publisher - Iron and Steel Institute of Thailand

Category - General Novel

Iron slag and steel slag are by-products generated simultaneously during smelting process of pig iron on a blast furnace and that of steel on an electric arc furnace, respectively. Even if slag is not considered as hazardous material, from an environmental point of view it is defined as waste. One main component of slag is silica, where as silicon is an essential micronutrient with several advantages in the growth of farm plants such as rice, sugar cane, cassava and corn. To fully utilize such silicon nutrient, the slag has to be processed to acquire a soluble form of silica, the so-called “ortho-silicic acid”. In the present work, innovative process for transforming slag to extract soluble silica in an active form has been developed. Soluble form of silica was prepared through an acid hydrolysis of slag concerned with acid conditions such as sulfuric acid system and a mixture system of perchloric acid and hydrochloric acid. Characterization of soluble silica compared with a commercial ortho silicic acid was performed by ATR FT-IR spectra analysis. Extractability of soluble silica was investigated by using inductively coupled plasma-optical emission spectrometry (ICP OES) and X-ray fluorescence spectrometry (XRF) techniques. The results showed that soluble silica in the form of ortho-silicic acid was productive when slag was processed with using sulfuric acid (H2SO4). By using a mixture of perchloric acid and hydrochloric acid, soluble silica was in the form of poly-silicic acid system. The obtained ATR FT-IR spectra of soluble silica were consistent with that of the commercial ortho-silicic acid. Absorption band of Si-O and Si-O-H, a prominent characteristic of ortho-silicic acid, were revealed at 1064 cm-1 and 984 cm-1 , respectively. Therefore, slag appears to be a promising source of using as fertilizer. 5.6% silicon could be extracted from iron slag in which a primary content of silicon is 14%. In steel slag, 3% silicon was extracted according to 11% of silicon content. This, however, needs furthers optimizing acid hydrolysis conditions to achieve a superior extractability of soluble silica.

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