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Uptake of Iron and Copper by Sorghum from Mine Tailings¹

ABSTRACT

Tailings from a lead-zinc-copper mine, representative of mine wastes in the Southwest, were reacted with sulfuric acid and ammonia to develop a product which has agricultural value for supplying trace elements, primarily iron. Iron-sulfur compounds (pyrites) are the dominant trace metal containing minerals. When reacted at 200C for 2 hours with concentrated H₂SO₄, the water-soluble Fe content of the tailings increases manyfold. The greater the amount of acid used, the greater was the soluble Fe. Water-soluble Cu also increased but to a very limited amount relative to Fe. Acid-treated tailings stimulated plant growth and Fe uptake by two varieties of sorghum (Sorghum bicolor L.), ‘Kafir’ and ‘Plainsman’, when these materials were supplied to an agriculturally important calcareous soil of the desert Southwest. The evidence developed points to a practical possibility of combining two waste products from the mining industry, stack-gas oxides of S (as H₂SO₄) and mine-tailing wastes, into usable agricultural products. The research further revealed significant growth responses to elemental S applied to soil which could not be duplicated with SO₄ ions. Growth response did not appear to be related to N, P, K, or Mn, Cu, or S deficiency of the soil. However, response was correlated with Fe and some factor(s) associated with acidification during oxidation of elemental S.

Key Words: sulfuric acid • sulfur • ammonium sulfate • ferrous sulfate • iron chlorisis • soil supplement

¹ Contribution from the Univ. of Arizona Agric. Exp. Sta., Tucson, AZ 87521. Journal Series Paper No. 2393. This research was supported in part by the Shattuck Denn Mining Corp., New York, and Iron King Mine, Humbolt, Ariz.

² Professor and former Graduate Assistant in Research, respectively. The latter's present address is Roseburg, Oreg.