Metal concentrate recovery

New chelating ion-exchange resins are able to selectively remove many heavy metals in the presence of high concentrations of univalent and divalent cations such as sodium and calcium. The heavy metals are held as weaMy acidic chelating complexes. The order of selectivity is Cu > Ni > Zn > Co > Cd > Fe + > Mn > Ca. This process is suitable for end-of-pipe polishing and for metal concentration and recovery. 

A widely used metal salt recovery technique is evaporation. With evaporation, plating chemicals are concentrated by evaporating water from the solution. Evaporators may use heat or natural evaporation to remove water.22 28 Additionally, evaporators may operate at atmospheric pressure or under vacuum. 

Additives often form a problem in recycling processes. Material recycling is often not possible or only with a considerable loss of quality. Plastics recycling is notoriously difficult due to the mixed composition of the plastics waste stream. The recycled material can only be used in certain applications that do not demand a pure material. Recycling of the additives themselves is theoretically possible only for metals, but in practice this type of recycling is not feasible. The metals occur only in low concentrations. Recovery from fly ash and bottom ash is possible, but expensive in view of growing scarcity problems it may become a viable options for at least some metals. 

The most recent studies [9] conducted on various base metal ores revealed some important features of flotation behaviour of gold from these ores. It has been demonstrated that gold recovery to the base metal concentrate can be substantially improved with the proper selection of reagent schemes. Some of these studies are discussed below. 

The flotation of Cu-Ni and Ni ores is discussed in Chapter 16 (Volume 1). In most operating plants, the emphasis is usually placed on Cu-Ni and Ni recovery and concentrate grade, and most of the research on these ores was directed towards improvement in Cu-Ni recovery and pentlandite-pyrrhotite separation, whereas little or no attention was paid to improvement in recovery of PGM. In operations from the Sudbury Region (Canada), PGM are recovered as by-products of Cu-Ni concentrates. The idealized flowsheet of the Inco Metal PGM recovery flowsheet is shown in Figure 18.4. 

Matte-slag-gas reactions in Cu-Fe-Ni sulphide ores. Sulphide ores are a major source of Cu, Ni and precious metals. A basic principle of the extraction processes is to blow air into the molten sulphide in order to oxidise (1) S, which forms a gas and (2) Fe, which forms predominantly FeO and then partitions to a slag phase which covers the matte. A key element in the recovery of the metals is the solidification of the matte which separates into a sulphur-rich matte and metal-rich liquid. This process may occur under non-equilibrium conditions with precious metals concentrating in the last metallic liquid. 

Holmium is obtained from monazite, bastnasite and other rare-earth minerals as a by-product during recovery of dysprosium, thulium and other rare-earth metals. The recovery steps in production of all lanthanide elements are very similar. These involve breaking up ores by treatment with hot concentrated sulfuric acid or by caustic fusion separation of rare-earths by ion-exchange processes conversion to halide salts and reduction of the hahde(s) to metal (See Dysprosium, Gadolinium and Erbium). 

According to the vendor, liqnid-liquid extraction (LLX) provides recovery, separation, purification, and concentration of metals in one unit process. By use of the proper extractant, metals can be reduced in process or waste streams to the low parts per million (ppm) level. The metals concentrated by the process can often be reused. When appropriate, specific metals can be recovered selectively in the presence of other metals or process stream components. Alternatively, broad-spectrum metal recovery is achievable with the properly selected extractant or process. 

A final illustration of the diverse applications of pyridines is given by 4-alkyl-2-mercap-topyridines (105), which are used in flotation processes for recovery of metal concentrates from metal-bearing ores (80BRP2046747). 

The latest projects to eliminate the production of waste treatment sludges were undertaken in the wet process metal plating production area. The projects, completed in March 1989, involved the installation of separate cadmium, chrome, copper and nickel recovery systems. All of the recovery systems utilized redundant conventional ion exchange columns for initial metal waste recovery and concentration. 

Environmental Applications mineral leaching, metal concentration, pollution control, toxic waste degradation, and enhanced oil recovery. 

This chemical inertia is, probably, also the reason for which its chemistry has played a minor role for many years. In fact, initially all its known chemistry was that related to the concentration, recovery, and purification of this element.1 Moreover, the chemistry of gold was merely regarded as an art to recover and convert gold metal into all possible forms for ornamental, monetary, anticorrosive, or electrical usage. It is therefore no surprise that the chemistry of gold, which is so clearly dominated by the metallic state, remained undeveloped for so long. 

The raw gas from the partial oxidation contains soot, about 0.8 wt% of the hydrocarbon feed. Soot particles together with ash are removed mainly in the venturi scrubber downstream of the quench. The soot slurry from quench and venturi is sent to the metals ash recovery system (MARS) Figure 58. First the soot slurry is flashed to atmospheric pressure and then filtered, leaving a filter cake with about 80 % residual moisture. The filter cake is subjected to a controlled combustion in a multiple hearth furnace. Under the conditions applied, a metal oxide concentrate containing 75 wt% of vanadium, together with some nickel and iron, is obtained which can be sold to metal reclaimers. The MARS ist practically autothermal as the heat of combustion is sufficient to evaporate the moisture of the filter cake. 

Scott [11] compared three types of circulating particulate electrodes for copper recovery from dilute solutions (Fig. 1) spouted (circulating) beds, vortex beds, and moving beds. The beds contained 500— 700 pm spherical copper particles positioned on a stainless steel cathode feeder, and a platinized titanium anode. All electrodes performed similarly in terms of copper recovery current efficiencies. Recovery was found to be more efficient at low pH and high metal concentrations. The spouted bed electrode was preferred on the basis of scaleup. 

A recent report by Haver et al. (H16) described the recovery of lead and. sulfur from a lead sulfide concentrate using ferric sulfate as the leaching reagent. Elemental sulfur was produced during the oxidation of lead sulfide to lead sulfate by hot ferric sulfate solution. The lead sulfate in the re.sidue was changed to acid-soluble lead carbonate by treatment with ammonium carbonate, and ammonium sulfate was a by-product. Hydro-fluosilicic acid dissolved the lead carbonate and an electrolysis step regenerated the HjSiF and deposited 99.9% pure lead metal. The recovery for lead was about 90% and for sulfur, 67%, half as elemental sulfur and the other half as ammonium sulfate. 

The importance of these secondary effects on acid-base status, metal concentration, and toxicity are still being studied. The recovery from acidification has been simulated by MAGIC for many watersheds, but sufficient time has not elapsed since acid inputs declined to assess the accuracy of the model predictions (Majer et aL, in review). 

Recovery of Metals Concentrate. The Sc-depleted raffmate from the ion exchange process step contains the two major constituents, Fe and Mn, in their divalent state, and other transition and rare metals in small amounts. The recovery of these metals in the presence of large amounts of Fe and Mn is done effectively by selective precipitation in the pH range between 6.5 and 7.5. In this experiment, the pH of the raffinate solution was adjusted with ammonium hydroxide to 7.4, and the resulting precipitate washed and dried. It contains the metals listed in Table VIII in a mattix of hydrated ferric oxide the precipitation of appreciable amounts of iron, about 14% of the iron content of the raffinate, is primarily due to the partial oxidation of the ferrous... 

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