Copper Industrial Byproducts for Improving Iron Deficient Calcareous Soils¹

Abstract

Laboratory and greenhouse experiments were conducted to evaluate an iron‐rich surplus by‐product (“jarosite”) from a copper refining process as Fe fertilizer. Combinations of H2SO4, which is a by‐product from copper smelting, with “jarosite” were studied in order to see if the iron solubility would be increased. Acidification of the “jaroste” greatly enhanced Fe solubility. As the “jarosite”/H2SO4 ratio increased from 1:1 to 7:1, the amount of the material solubilized as Fe decreased from approximately 12 to 2%. At ratios wider than 7:1, negligible amounts of Fe dissolved. At “jarosite”/H2SO4 ratios < 1, Fe solubility increased but the end product could not be handled as a conventional pelleted or powdered fertilizer. In greenhouse experiments using sorghum (Sorghum bicolor ‘Double Dwarf Yellow Sooner’) in an Fe‐deficient calcareous soil, the 2:1 mixture of “jarosite”/H2SO4 was significantly more effective than either “jarosite” or H2SO4 alone in terms of increasing plant growth and chlorophyll content. The mixture compared favorably with conventional inorganic and chelated sources of Fe. Varying the ratio of “jarosite”/H2SO4 from 1:1 to 5:1 resulted in no differences in yield. Particle size of the mixture influenced plant growth. The < 1 mm fraction was most effective, the 1 to 2 mm and 2 to 6 mm fractions gave similar yields and the 6 to 12 mm fraction was least effective. Post‐harvest analysis of the cropped soil showed that the “jarosite”/H2SO4 mixture significantly increased the levels of DTPA‐extractable Fe.

Increasing Iron Availability to Crops: Fertilizers, Organo-Fertilizers, and Biological Approaches

“…Low-grade pyrite (FeS,) from mining residues, Fedust from the steel industry, coal slurry solids, and some other waste and by-product materials are often an avail-able source for large quantities of low-priced Fe minerals. In many areas where Fe-deficient fields are close enough to a source of such materials, attempts have been made to make use of the available Fe-source by applying it to soil (Hagstrom 1984;Ryan and Stroehlein 1976;Wallace et al 1976). These materials were found, however, to face the same problems as those previously discussed.…”

“…Thus, inorganic Fe-compounds are all of limited value in highly calcareous soils that tend to induce severe Fe-deficiency. Decreasing particle size, acidification, and band application rather than surface broadcast, may slightly increase the effectiveness of these materials (Hagstrom 1984;Ryan and Stroehlein 1976;Vlek and Lindsay 1978).…”

Highly variable conditions and responses pose problem in product development

“…Greenhouse studies at the University of Arizona (Ryan and Stroehlein, 1976) demonstrated the potential effectiveness of this product. Subsequent greenhouse and field research during the past seven years has often given positive responses (Marsolek and Hagstrom, 1982); however, the desired level of consistent responses hoped for has not always been obtained.…”

“…A co-produced mining residue contains high levels of water insoluble iron and sulfur compounds. However, when reacted with sulfuric acid, much of the iron is solubilized and a resulting highly acidic material has been developed which often gives positive results in the treatment of chlorosis (Ryan and Stroehlein, 1976). Research using this material has been conducted for 7 years and the product which evolved is presently being produced and sold under the trade name of Iron-Sul, and hereafter will be referred to as such.…”

Grain sorghum response to plant residue‐recycled iron and other iron sources

“…Ryan and Stroehlein (1976) showed .that copper mining residues can be effective Fe sources when treated with acid. Subsequent work by Vargas-Morales (1979) indicated similar acidified mining residue can alleviate Fe chlorosis on sorghum under greenhouse conditions.…”