1986-12-08_GENERAL DOCUMENTS - M1977493 (2)

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14 Breaking the dormancy of Indian ricegrass seeds offers substantial prom- ise for initiating this type of growth on adverse tailing materials, thus offering the potential of reducing nitrogen fertilizer requirements and related maintenance costs. Stands of Indian ricegrass are normally short- lived, but should prepare the way for accession of other plants. Tests are underway to determine if properly treated seeds can be germinated and growth sustained in adverse tailing materials. Vegetating Adverse Tailings Practically all mill tailings contain deleterious inorganic salts, lack organic components and essential nutrients, and do not have the physical nature required for sustaining vegetative growth. For many tailings these adverse conditions can be overcome in time by fertilization, gradual buildup of organic and microbial populations by encouraging plant growth, and use of chemicals for binding of the surface to prevent blowing of loose sands that cut off or bury established vegetation. However, excessive salinity or acid- ity presents more difficult problems. Combination problems can exist in which tailings may be excessively saline, because of the recycling of processing waters, and simultaneously contain sulfide materials such as pyrite that upon oxidation would drop the pH of the tailings to a low level in a- relatively short time. Such a tailing is Kennecott's Utah Copper Division milling waste. This material with a pH of 7.8, when fresh, contains salinity equivalent to 2.4 atmospheres osmotic concentration plus approximately 1.3 percent pyrite. The salts in the tailings cause an osmotic gradient that transfers fluid from the plants and thus vegetation dies of dehydration shortly after sprouting. Another problem is that , if vegetation is planted on these tailings and irri- gation of the plants leaches away the salts, the pyrite oxidizes and the pH may drop from 7.8 to less than 3.0 within a month's time. Therefore, this material was considered as a typical adverse waste and was used for laboratory and small field testing. Salinity and Heavy Metal Salt Problems Salts present in the wastes or mill waters impede plant growth. Consid- erable difficulty was encountered in growing vegetation in milling wastes from Kennecott's Utah Copper Division. To determine the reasons, duplicate plant- ings were made in (1) the normal flotation tailings, containing considerable water-soluble salts,but assaying only 0.05 percent copper, and (2) a simulated tailing containing few soluble salts but almost 0.25 percent copper. In both materials the copper was present mainly as the sulfide mineral, chalcopyrite. Seeded test plots were watered'with tapwater and tailings effluent water. Both germination and growth were adversely affected when effluent water was used. For samples watered with tapwater, germination and growth were much better in the simulated tailing material despite the higher content of copper. These tests indicated that the toxicity was due primarily to the high salt con- tent of the water and tailings. Supplementary tests were made to determine which salts or organic reagents in the copper mill tailings solutions most affected plant growth. The tailings water was compared with a prepared solution simulating saline but