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18 <br />of a fine water spray, described earlier, provides another technique which may <br />be effective for controlling excess acidity. <br />Tailings samples from several locations would not support vegetation <br />without neutralization. Among these were uranium tailings from Wyoming and <br />Colorado which had respective pH values of 2.3 and 4.5. Addition of JO and <br />7 pounds of lime per acre, respectively, added to the top 2 inches of tailings <br />raised the pH to a level high enough to sustain plant life. The tailings pile <br />at the site of the former Vitro Minerals & Chemical Co., Salt Lake City, Utah, <br />contains both acidic uranium tailings (pH 3.6) and basic vanadium tailings <br />(pH 8.5). These were mixed in the laboratory in equal portions to produce a <br />material of pH 6.3 in which seeds readily germinated. Fertilization, however, <br />was necessary to sustain adequate plant growth. <br />Alterin& the Structure and Organic Composition of Tailings <br />As previously noted, fine mineral wastes lack nutrients, humus, and micro <br />bial populations all of which militate against the growth of vegetation. They <br />may also lack the proper surface structure for air and water access and resist <br />ance to being blown or washed away. Coarse grains and mineral aggregates are <br />of importance on the surface of beach and pond areas of tailings accumulations <br />because they resist movement by wind and water, Coarse grains and aggregates <br />are of even greater benefit to stability.on the sloping dikes of the tailings <br />ponds. Fertile soil in which vegetation grows most abundantly, unlike mill <br />tailings, usually contains a small but important percentage of organic matter <br />and micro-organisms. Plants can be grown well in pure sand cultures to which <br />have been added a proper balance of all the necessary mineral compounds needEs <br />by the plant, but if a little appropriate organic matter, such as leaf mold, <br />is added, the plants grow much better. To prepare synthetic soils from barren <br />tailings, research was conducted using additions of chemicals, sewage sludge, <br />and compost, <br />Structural and Organic Modifications of Tailings <br />Several methods were tried for increasing particle aggregation of tail- <br />ings to provide better root environment and soil aeration, thereby improving <br />vegetative growth. Effective pelletizing and agglomerating procedures were <br />developed. One of these procedures consisted of pelletizing tailings to <br />minus-8-plus-35-mesh size with 2.5 percent asphalt, hardening the pelleCs by <br />baking at 250° C, and spreading the pellets over the surface of the tailings <br />to a depth of 1/2 inch, or mixing the pellets with an equal quantity of tail- <br />ings to form a 1-inch-deep covering over normal tailings. A similar pellet <br />was prepared, without the baking step, by pelletizing with 3 to 4 percent <br />Peneprime (a commercial asphaltic bitumen product cut with white kerosine) or <br />with 1 to 2 percent Coherex. Another procedure not requiring pelletization <br />encompassed (1) seeding, (2) watering, (3) raking the wet tailings to form <br />small-size agglomerates, and (4) spraying the agglomerates with Coherex and/ox <br />Soil Gard to preserve the pelletized form. Plant growth was improved in all <br />instances where a granular, soillike texture was achieved by these methods. <br />Additionally, two types of municipal wastes were tested as addi[ives to <br />tailings. One was a commercial compost made from municipal refuse, and the <br />