Wastes metal/mineral recovery from

Nonferrous Metal Production. Nonferrous metal production, which includes the leaching of copper and uranium ores with sulfuric acid, accounts for about 6% of U.S. sulfur consumption and probably about the same in other developed countries. In the case of copper, sulfuric acid is used for the extraction of the metal from deposits, mine dumps, and wastes, in which the copper contents are too low to justify concentration by conventional flotation techniques or the recovery of copper from ores containing copper carbonate and siUcate minerals that caimot be readily treated by flotation (qv) processes. The sulfuric acid required for copper leaching is usually the by-product acid produced by copper smelters (see Metallurgy, extractive Minerals RECOVERY AND PROCESSING). 

Brookhaven National Laboratory s (BNL s) biochemical recovery of radionuclides and heavy metals is a patented biochemical recovery process for the removal of metals and radionuclides from contaminated minerals, soil, and waste sites. In this process, citric acid, a naturally occurring organic complexing agent, is used to extract metals and radionuclides from solid wastes by the formation of water-soluble, metal-citrate complexes. The complex-rich extract is then subjected to microbiological biodegradation that removes most of the extracted heavy metals. 

TBP, (BuO)3PO, and related esters such as dibutyl phosphate, (BuO)2P(0)OH (DBP), and bis-2-ethylhexyl phosphate (HDEP) find important uses in the extraction of rare earth, actinide and other heavy metals from mineral sources, and their recovery from waste products of the atomic energy industry. A solution of TBP in kerosine... 

Metal items constitute an appreciable amount of solid waste, with their percentage varying between 5 and 15 percent in most cases. As the revenue from solid-waste processing plants is derived from the sale of the separated products, among which ferrous and nonferrous metal items, the recovery and recycling of metallic objects support considerably the construction and operation of solid-waste treatment plants. The recycling of metal items is very important, as it contributes in mineral deposits conservation and in the prevention of environmental pollution from the oxidation and dissolution of various metals, being in alloyed form. 

R. J. Wilson, T. J. Veasey and D. M. Squires, "The Application of Mineral Processing Techniques for the Recovery of Metal from Post-consumer Wastes , Minerals Engineering J., 7 (8), 975-984 (1994). 

Thirty-four minor and trace elements are of potential environmental concern (n ). Sulfur is the element of major concern due to its abundance in flue gases from some coal-burning plants and its subsequent contribution to "acid rain." Sulfur as acidic ions of sulfate can also contribute to pollution of surface water and groundwater. Other elements of greatest concern are As, B, Cd, Pb, Hg, Mo, and Se. With the exception of B and Se, these elements are strongly associated with mineral matter in the coal and are concentrated in waste piles from coal preparation plants. If the waste disposal site is not constructed as a closed system, pollution of nearby groundwater is possible. Boron and Se may contribute to the pollution risk as they are associated with both mineral and organic components. On the other hand, certain coal-mine wastes have potential for recovery of valuable metals such as zinc and cadmium (18). 

Acid-containing wastes are produced in many industries. Thus, in leaching of minerals, in regeneration of cation exchangers, and in metal surface treatment, only a part of the acid is utilized (due to the reduced activity at the lower acid concentration). The acids plus salts comprising aqueous solutions formed in these operations as well as in others (e.g., zinc electrowinning) are neutralized in most cases and disposed of. Efficient separation and recovery of the acid values is more beneficial, as it would save on acid and base consumption, reduce discharge of solution or solids, and enable recovery of other valuable components (e.g., metal values) from the deacidified solutions. 

There are two other aspects that should be mentioned here that may directly affect the choice of the milling process. First, the uranium ore often contains other metals that have commercial value, like vanadium or niobium, for example, and their recovery may influence the process selected for uranium recuperation. Second, uranium itself may be a by-product of other processes like gold extraction, niobium, and tantalum production or phosphoric acid manufacture. Thus, recovery of low levels of uranium from phosphates, columbite, or gold-bearing minerals may not be economical in itself, but extracting uranium as a by-product from the waste streams of these operations could be commercially sensible. 

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