Abstract
Silica is a nutrient for diatom, which is a phytoplankton in oceans. We thus study the possibility of generating silica from steelmaking slag. Silicic acid present in steelmaking slag comprising of sodium chloride was examined. When non-carbonated slag and carbonated slag sample in solutions consisting of 0.5 mol dm–3 sodium chloride were shaken for a week, a slightly higher pH for carbonated slag solution was observed. The concentration of extracted silicic acid from carbonated slag was higher than that from non-carbonated slag. Both solutions contained high concentrations of calcium ions.
Silicic acids show several chemical forms in solutions. The silicic acids contained in both non-carbonated and carbonated slag solutions were identified with FAB-MS (fast atom bombardment mass spectrometry): [Si(OH)2O2Na]–, [Si(OH)O3Ca]–, [Si2(OH)5O2]– ([dimer]–), [Si2(OH)4O3Na]–, [Si4(OH)7O5]– ([cyclic tetramer]–), [Si4(OH)6O6Na]–, [Si4(OH)9O4]– ([linear tetramer]–), and [Si4(OH)8O5Na]–. Among all these complexes the diatom uptakes [dimer]–, and [linear tetramer]–. The silicic acids in both solutions also showed almost the same peak intensity ratios of [Si(OH)2O2Na]–, [Si(OH)O3Ca]–, [dimer]–, and [linear tetramer]– against [cyclic tetramer]. As a result, we consider carbonated slag to be a better supplier of silica to seawater than non-carbonated slag.
