Precipitation mineral processing

The concentrations of other metals attenuate when the metals sorb onto the surfaces of precipitating minerals (see Chapter 10). Hydrous ferric oxide, the behavior of which is well studied (Dzombak and Morel, 1990), has a large specific surface area and is capable of sorbing metals from solution in considerable amounts, especially at moderate to high pH HAO may behave similarly. The process by which hfo or HAO form and then adsorb metals from solution, known as coprecipitation, represents an important control on the mobility of heavy metals in acid drainages (e.g., Chapman etal., 1983 Johnson, 1986 Davis etal., 1991 Smith et ai, 1992). 

Sulfate, halide, and carbonate minerals form in mine waste as a result of chemical weathering reactions and as a by-product of mineral processing. The formation of carbonate minerals is of particular interest for its potential in offsetting greenhouse gas emissions associated with mining. We have documented secondary carbonate mineral precipitation at the Mount Keith Nickel Mine (Western Australia) and the... 

O Dell, C. S., Walker, G. W., Richardson, P. E., 1986. Electrochemistry of the chalcocite-xandiate system. J. Appl. Electrochem., 16 544-554 Opahle, I., Koepemik, K., Eschrig, H., 2000. Full potential band stracture calculation of iron pyrite. Computational Materials Science, 17(2 - 4) 206 - 210 Page, P. W. and Hazell, L. B., 1989. X-ray photoelectron spectroscopy (XPS) studies of potassium amyl xanthate (KAX) adsorption on precipitated PbS related to galena flotation. Inter. J. Miner. Process, 25 87 - 100... 

It will be apparent that if normal extracellular fluids were subjected to an isotonic resorption of sodium and chloride ions by the process, the net effect would be to concentrate other ions and precipitate minerals. This suggestion was made613 to explain one of the methods of forming deposits in the calciferious glands of earthworms. It was proposed that the posterior glands received blood directly from the intestine. Fluid was formed in these glands by a process of filtration and saline was then resorbed by the epithelial cells. This resulted in the formation of calcareous deposits (Fig. 5). 

The insoluble Ca(II) salts of weak acids, such as calcium phosphate, carbonate, and oxalate, serve as the hard structural material in bone, dentine, enamel, shells, etc. About 99% of the calcium found in the human body appears in mineral form in the bones and teeth. Calcium accounts for approximately 2% of body weight (18,19). The mineral in bones and teeth is mosdy hydroxyapatite [1306-06-5] having unit cell composition Ca10(PO4)6(OH)2. The mineralization process in bone follows prior protein matrix formation. A calcium pumping mechanism raises the concentrations of Ca(II) and phosphate within bone cells to the level of supersaturation. Granules of amorphous calcium phosphate precipitate and are released to the outside of the bone cell. There the amorphous calcium phosphate, which may make up as much as 30—40% of the mineral in adult bone, is recrystallized to crystallites of hydroxyapatite preferentially at bone collagen sites. These small crystallites do not exceed 10 nm in diameter (20). 

Land disturbance and exposure of buried geologic strata to the open environment leads to sulfide oxidation (if present) and, as a consequence, water-quality degradation of runoff. For water-quality-control purposes, sedimentation ponds required by law are used as water treatment basins. Often, the pH of such basin waters is below 6, and the concentration of heavy metals is above acceptable levels. Water treatments include neutralization and removal of heavy metals as precipitates. Similar water-quality problems arise from other industrial sources, including heavy steel industries, electronics, food processing, mineral processing, and waste-disposal leachates. This portion of the chapter deals with some of the chemical agents used for neutralization purposes and some of their limitations. 

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