Recovery of Valuable Metal

Sodium Tetrahydroborate, Na[BH ]. This air-stable white powder, commonly referred to as sodium borohydride, is the most widely commercialized boron hydride material. It is used in a variety of industrial processes including bleaching of paper pulp and clays, preparation and purification of organic chemicals and pharmaceuticals, textile dye reduction, recovery of valuable metals, wastewater treatment, and production of dithionite compounds. Sodium borohydride is produced in the United States by Morton International, Inc., the Alfa Division of Johnson Matthey, Inc., and Covan Limited, with Morton International supplying about 75% of market. More than six million pounds of this material suppHed as powder, pellets, and aqueous solution, were produced in 1990. 

The recovery of valuable metals and metal alloys from hazardous metal sludges is technically and economically viable. Small quantities of excess slag are produced and this slag can be recycled into concrete blocks. The E.P. and TCLP leachate limits are met with the slag. 

Boyadzhiev L. Recovery of valuable metals from diluted aqueous solutions by creeping film pertraction. In Devis GA Ed. Separation Processes in Hydrometallurgy. London 1987 Pt. 3, Ch. 26 259-287. 

Many commercial cell types can be used for metal recovery. The cells are based on different concepts, and the process objectives may be recovery of valuable metal, metal removal from the effluent to meet discharge requirements, and so on. Some of the developed and commercialized cell types include the following [3] ... 

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). 

NATANSOHN ITT AL. Recovery of Valuable Metals from Industrial Wastes 133... 

Because of their salt-like structure, the quaternary ammonium salts enable a selective continuous separation of phosphine oxides and degradation products during the hydroformylation reaction and thus a prolongation of catalyst life-time [38]. The amine backbone can be re-used. The finally recovery of valuable metal, anions, or cations is possible by simple neutralization reactions. 

Hydrometallurgy makes use of redox and complexation reactions for the recovery of valuable metals from ores. This is exemplified by the dissolution of gold metal in ores through oxidation by air and complexation by cyanide. 

Recovery of valuable metals from secondary sources. At the present state of development the more promising metal recovery processes based on SIR systems appear to be in the following applications in terms of both process performance and economic considerations (a) Recovery of metals from dilute solutions, particularly where such solutions are available at low cost (e.g., waste solution from other processes, mine waters, or dump leaching solutions) (b) separation of metals from concentrated solutions obtained by hydrometallurgical processing of complex ores, concentrates, mattes, and scraps and purification of process solutions (such as electrolytes) which may contain a variety of metals that have been only partially recovered in the conventional processing steps (c) separation and purification of met-... 

Perhaps the most cost effective use of flotation techniques would lie in recovery of valuable metals from the wastewaters generated in the photographic, electroplating, and jewelry manufacturing industries. 

Liquid membranes possess a number of advantages over solvent extraction methods for the recovery of valuable metals from dilute aqueous solutions. These include the following ... 

Environmental requirements are assuming great importance, since there is an increased interest in the industrial use of renewable resources such as starch and chitin. Considerable efforts are now being made in the research and development of polysaccharide derivatives as the basic materials for new applications. In particular, the increasing cost of conventional adsorbents undoubtedly makes chitin and chitosan-based materials one of the most attractive biosorbent for wastewater treatment. Chitin and chitosan biopolymers have demonstrated outstanding removal capabilities for certain pollutants such as dyes and metal ions as compared to other low-cost sorbents and commercial-activated carbons. Biopolymer adsorbents are efficient and can be used for the decontamination of effluents (removal of pollutants) and for separation processes (recovery of valuable metals). 

The high sorption capacities of modified chitosan for metal ions can be of great use for the recovery of valuable metals (or) the treatment of contaminated effluents. A great number of chitosan derivatives have been obtained with the aim of adsorbing metal ions by introducing new functional groups onto the chitosan backbone. The new fimc-tional groups are incorporated into chitosan to increase the density of sorption sites. 

Keywords Vacuum distillation Multi-component of alloys of silver. Renewable resources Recovery of valuable metal... 

Zhaofeng Xie. Recovery of Valuable Metals from Jamesonite with United Pyro- and Hydrometallurgical Process, Doctor Degree Thesis, Central South University, Changsha,... 

---