Leaching metal concentration

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

One, the CLEAR process, was investigated by Duval Corporation near Tucson, Arizona (29). It involves leaching copper concentrated with a metal chloride solution, separation of the copper by electrolysis, and regeneration of the leach solution in a continuous process carried out in a closed system. Elemental sulfur is recovered. Not far from the Duval plant, Cypms Mines Corporation operated a process known as Cymet. Sulfide concentrates undergo a two-step chloride solution leaching and are crystallized to obtain cuprous chloride crystals. Elemental sulfur is removed during this stage of the process. 

The basic structure of the catalysts was not changed on the conditions of modification from the XRD patterns shown in Fig. 2. From the ICP analysis, it was observed that impregnated concentration of transition metals on the surface of Ti02 were consistent with leached solution concentration. 

Scarponi et al. [93] concluded that filtration of seawater through uncleaned membrane filters shows positive contamination by cadmium, lead, and copper. In the first filtrate fractions, the trace metal concentration maybe increased by a factor of two or three. During filtration, the soluble impurities are leached from the filter, which is progressively cleaned, and the metal concentration in the filtrate, after passage of 0.8 -11 of seawater, reaches a stable minimum value. Thus it is recommended that at least one litre of seawater at natural pH be passed through uncleaned filters before aliquots for analysis are taken... 

The critical metal leaching rate depends on critical dissolved metal concentrations, which can be derived in different ways, for instance as a critical limit for soil solution (see above). 

Skeletal (Raney ) catalysts are made by a very simple technique. An alloy of two metals in roughly equal proportions, where one metal is the desired catalytic material, and the other is dissolvable in hydroxide, is first made. This alloy is crashed and leached in concentrated hydroxide solution. The soluble metal selectively dissolves, leaving behind a highly porous spongelike structure of the desired catalytic metal. Catalysts formed by this technique show high activity and selectivity, and have found wide use in industry, particularly for hydrogenation and dehydrogenation reactions. 

The widespread use of platinum, palladium and other metals in automotive catalytic converters has been driven by environmental considerations and the increasing costs of the metals. This has not been matched by the development of clean reprocessing technologies for the catalysts themselves. The spent catalyst metals are oxidized to their cations via leaching into concentrated acids. 

The concentrated molybdenite ore is then roasted in air, converting molybdenum sulfide to molybdenum trioxide M0O3. This is harvested in high purity by sublimation. An alternative is to leach molybdenite concentrate with dilute ammonia solution, which converts the metal to ammonium molybdate, (NH4)2Mo04. Molybdenum trioxide or ammonium molybdate product is then heated with hydrogen at elevated temperatures from 500 to 1,150°C in a furnace to produce molybdenum powder. 

BA and FA of conventional low-temperature incineration usually leads to much higher metal concentrations, commonly exceeding permissible values, when leached under the conditions of the Swiss leaching test (ABB-EAWAG-EMPA-KEZO 1990 EKESA 1992). 

The data shows an immediate decrease (the difference between untreated and 0 hours after treatment) in the TCLP leachable metals concentration for all seven metals. This indicated that the metals were bound immediately upon being treated. There would be no threat for contaminant leaching during the period it took for the CHEMFIX product to physically solidify. In addition, the TCLP leachable metal concentrations of those samples that were not allowed to cure (0 hours after treatment) all passed the TCLP regulatory limits. Therefore immediately after treatment the material can be classified as non-hazardous. 

In this experiment, ex situ soil colloids with diverse mineralogical composition after equilibration with metal solutions of known concentrations were leached through undisturbed soil monoliths exhibiting considerable macroporosity. The colloids (<2 pm) were separated from upper-soil Bt horizons with montmorillo-nitic, illitic, and kaolinitic mineralogy. The equilibration metal solutions contained Cu, Zn, and Pb. Eluents were monitored over ten pore volumes for colloid and metal concentrations. 

The leaching solutions/suspensions were applied to the top of each monolith through a continuous step input of 2.2 cm/h-1 controlled with a peristaltic pump. This rate was tested in earlier experiments and found to provide consistent freeflow conditions without ponding on the top of the monoliths. All input mixtures were allowed to equilibrate for 24 h before application. For -10 days, eluents were monitored with respect to volume, colloid, and metal concentration. BTCs were constructed based on reduced metal and colloid concentrations (C/CG) and pore volumes. 

An example of a noncovalent attachment of a metal-phosphine complex to a solid support is presented in Figure 31, as reported by Bianchini et al. (120). The complex is attached via a sulfonated variant of the "triphos" ligand, which is known for its successful application in several catalytic reactions. The ligand is attached to the silica by an ionic bond, which is stable in the absence of water. The catalyst was used for the hydroformylation of styrene and of hex-1-ene in batch mode and showed moderate activity. The triply coordinated rhodium atom is strongly boimd although the conditions were rather harsh (120 °C, 30 bar) the concentration of leached metal measured by atomic emission spectroscopy was at most at the parts per million level. However, for commercial applications, for example, in a process such as hydroformylation of bulk products, these concentrations should be less than 10 ppb 111,121). 

The concentrations of lead, zinc, copper, mercury, and several other metals (excluding iron and manganese) are almost always very low (<1 mg L ) in oil-field waters, because they are limited by the very low solubility of their respective sulfide minerals. Exceptionally rich sources of metals such as redbeds are probably present in the few localities worldwide, where dissolved metal concentrations are high. Metals leached from these beds precipitate along with available reduced sulfur dissolved metal concentrations increase to high values only when the concentration of H2S is extremely low (<0.01 mg L ). 

Fig. 9. shows the concentrations of metals leached from the particles as a function of the total amount of acid passed through the column for one experimental run. The release of metals into the leachate water leaving the columns containing small particles did not occur until after addition of about 8 meq acid/g waste. Metal concentrations in the leachate then increased rapidly for a time before... 

A study of the leaching ability of metals from plastics is important particularly where children s toys, foods and pharmaceuticals are concerned. A potential plastic to be used for any of these products must be analysed for total and leaching metal content by contacting the plastics with a stimulant similar to the product. Such plastics are strictly monitored and are rejected if a trace concentration of one or more listed toxic elements is detected. 

In our case the solid residues contained approx. 12 % organic carbon. The heavy metal concentrations were low, probably and primarily due to the low quantities of such substances in the input material. Leaching experiments showed that the drum reactor residues yielded mainly chloride-and sulphate-containing extracts. The chemical oxygen demand of these solutions was relatively high when compared with the BOD. 

Estimating metal leaching flux from the ecosystem, we proposed to protect the drinking groundwater and surface water. We supposed that metal concentration in the... 

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