Soil additives calcium sulfate

HPT Research, Inc., has developed the ionic state modification (ISM) process for the treatment of acid mine drainage (AMD). ISM is an ex situ treatment technology that uses magnets, electricity, and proprietary chemical to precipitate heavy metals, remove sulfate ions, and neutralize acidity from AMD and industrial wastewaters. The end products of the process are a metal hydroxide sludge, a calcium sulfate sludge, and treated liquid effluent. The vendor claims that the metal hydroxide sludge may have some value as an ore, the calcium sulfate may be used as an agricultural additive to soils, and the liquid effluent is free of metal contamination and has low sulfate concentrations. 

An official procedure [10,11] describes a method for the determination of chloride in a saturated calcium sulfate extract of soil. The extract is acidified and the concentration of chloride is determined by titration with mercuric nitrate using diphenylcarbazone as indicator. Mercuric ion in the presence of chloride forms mercuric chloride, which, although soluble, provides insufficient mercuric ion to form the mercuric-diphenylcarbazone complex. When all of the chloride has been removed in this way, addition of further mercuric ion produces the violet complex. 

In addition to the conventional listing of major constituents, a commercial blend may be formulated to contain one or more of the secondary constituents, calcium, magnesium, or sulfur, which are used to correct local soil deficiencies. These are normally specified in a separate listing. The importance of these, too, cannot be overlooked as, for example, fertilization of a sulfur deficient soil with soluble sulfate has given over 1100% rapeseed (canola) crop improvement [69]. 

The development of a good agricultural soil from an alkali soil consists in establishing adequate drainage and in the addition of soluble calcium and magnesium in such amounts, by methods that will assure that these added elements will replace much of the sodium adsorbed on the exchange complex. The kind of substance added varies with the soil, cost, and local conditions. Among those used are calcium chloride, calcium sulfate, calcium carbonate, aluminum sulfate, iron sulfate, sulfur and sulfuric acid. 

In a comparison of how N fertilizers that also contained S affected the elemental composition of celery (Apium graveolens) grown on polluted marsh soil, Schnug and Schnier (1986) observed that with the use of ammonium sulfate (as compared with urea or calcium ammonium nitrate) there was a conspicuous increase in total S, accompanied by a significant decrease in Mo concentration of up to 80% (Figure 15.1). In soils that are inherently poor in available Mo, or where its availability is limited by acid conditions, addition of S fertilizer may further aggravate... 

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