Quenched Calcium Silicate Slag and Limestone Incorporations in Two Tennessee Soils — A 10‐Year Lysimeter Study

Incorporations of glassy quenched Ca‐silicate slag from rock phosphate‐reduction furnaces and limestone were compared by means of a 10‐year lysimeter experiment on acidic fallow Hart‐sells fine sandy loam and Baxter silt loam. Annual composites of periodic collections of rainwater drainages were analyzed for contents of Ca, Mg, K, P, S, N, and fluorine. Variables were particle size, rates for single and repetitive inputs, and depth of incorporation. After 10 years, all eight 2‐ton slagged and limestoned soil systems had lost half of the calcium input, there were no carbonate residues, and soil pH was 6.3. The four repetitive 2‐ton inputs caused increases of 3 to 4 times in calcium outgo, and every outgo from the slag was decidedly larger than the corresponding outgo from the limestone. Calcium outgo from full‐depth incorporations of slag was about twice the outgo from half‐depth incorporations. Ca‐bicarbonate outgo from the slag always exceeded that from the limestone, although the requirements of CO 2 for the production of the bicarbonate from the slag were twice the requirements for the dissolving of the limestone. Residues of carbonate engendered from 8‐ton incorporations of slag were small, although enhancements of 4 ½ tons in outgo of CaCO 3 , as bicarbonate, had occurred. Residues of CaCO 3 , engendered from 20‐ton inputs of the silicate of the slag, were 9 tons and 10 tons from Hartsells and Baxter soils, respectively. Because of its porosity and its speedy hydrolytic transition and the sequential carbonatation of any fraction of the Ca(OH) 2 that was engendered but not sorbed directly by the soil, the heavy‐rate inputs of slag induced Ca‐outgo increases far beyond the increases from limestone. The heavily slagged soils acquired substantial accumulations of engendered CaCO 3 , and pot cultures demonstrated that such accumulations induced fertility. Magnesium outgo and potassium outgo were lessened by the slag and by the limestone in both soils. Nitrate and sulfate leachings were increased by all incorporations of slag and of limestone. The lightly‐slagged soils yielded relatively small increases in fluorine outgo, but the 796‐pound maximal recovery represented 52% of the fluorine carried by the heavy‐rate incorporations of slag. Outgo of fluorine, along with calcium, from full‐depth incorporation of slag was substantially greater than such outgo from half‐depth incorporation. Phosphorus content of the slag was leached to significant extent. The detailed findings and the accelerative effect that the slag‐derived solvated silica exerts upon leachings of Ca, PO 4 , and fluorine will be reported elsewhere. It is believed that rational‐rate incorporations of the fluoride‐bearing quenched slag would not cause a harmful occurrence of fluorides in the waters of nearby wells and streams.