Leaching battery

In the leaching battery of Figure 14.19(a), the solids are transported between vessels with slurry pumps and are mixed in line... 

In the leaching battery of Figure 14.20(a), the solids are transported between vessels with slurry pumps and are mixed in line with countercurrent solution from the next stage. For the process to be effective, the solids must settle freely. The tanks have sloped... 

Additional areas for growth are expected to be ia copper leaching, caprolactam, pulp and paper, methyl methacrylate, and batteries (144). 

Batch Percolators The batch tank is not unlike a big nutsche filter it is a large circiilar or rectangiilar tank with a false bottom. The solids to be leached are dumped into the tank to a uniform depth. They are sprayed with solvent until their solute content is reduced to an economic minimum and are then excavated. Countercurrent flow of the solvent through a series of tanks is common, with fresh solvent entering the tank containing most nearly exhausted material. In a typical ore-dressing operation the tanks are 53 by 20 by 5.5 m (175 by 67 by 18 ft) and extract about 8200 Mg (9000 U.S. tons) of ore on a 13-day cycle. Some tanks operate under pressure, to contain volatile solvents or increase the percolation rate. A series of pressure tanks operating with countercurrent solvent flow is called a diffusion battery. 

During the first trials with synthetic separators around 1940 it had already been observed that some of the desired battery characteristics were affected detrimentally. The cold crank performance decreased and there was a tendency towards increased sulfation and thus shorter battery life. In extended test series, these effects could be traced back to the complete lack of wooden lignin, which had leached from the wooden veneer and interacted with the crystallization process at the negative electrode. By a dedicated addition of lignin sulfonates — so called organic expanders -— to the negative mass, not only were these disadvantages removed, but an improvement in performance was even achieved. 

Stationary batteries serve predominantly as an emergency power supply, i.e., they are on continuous standby in order to be discharged for brief periods and sometimes deeply, up to 100 percent of nominal capacity, in the rare case of need. The following profile of requirements for the separator thus arises very low electrical resistance, low acid displacement, no leaching of substances harmful to float-... 

For making fertilizer, in petroleum rehning, synthetic rubber and other plastics, copper leaching, manufacture of inorganic pigments, water treatment chemicals, paints, car batteries, etc. 

To conclude this section, reference may be drawn to what is called the Placid process for recycling lead from batteries. Placid denotes the leaching of lead in warm, slightly acidic, hydrochloric acid brine to form soluble lead chloride. Lead is won from the lead chloride on the cathode of an electro winning cell and is collected. Chloride anions are released simultaneously, but then react immediately with hydrogen ions that have been produced stoichio-metrically from electrolysis of water in the anolyte and passed into the catholyte through a membrane. The hydrochloric acid that is formed is returned as a make-up content to the leaching bath. 

However, there is one exception to using the TCLP to identify a waste as hazardous. The DC Circuit Court, in Association of Battery Recyclers vs. U.S. EPA, vacated the use of the TCLP to determine whether manufactured gas plant (MGP) wastes exhibit the characteristic of toxicity. As previously stated, the TCLP replicates the leaching process in municipal landfills. The court found that U.S. EPA did not produce sufficient evidence that co-disposal of MGP wastes from remediation sites with municipal solid waste (MSW) has happened or is likely to happen. On March 13, 2002, in response to the court vacatur, U.S. EPA codified language exempting MGP waste from the toxicity characteristic regulation. 

In landfills, heavy metals have the potential to leach slowly into soil, groundwater, or surface water. Dry cell batteries contribute about 88% of the total mercury and 50% of the cadmium in the MSW stream. In the past, household batteries accounted for nearly half of the mercury used in the United States and over half of the mercury and cadmium in the MSW stream. When burned, some heavy metals such as mercury may vaporize and escape into the air, and cadmium and lead may end up in the ash. 

Leaching of chemicals from complex materials or matrices is a complicated phenomenon in which many factors may influence the release of the specific organic compounds and inorganic ions. Important factors include major element chemistry, pH, redox, complexation, liquid to solid ratio, contact time, and biological activity. To describe fully the leaching of SWMs/COMs under field conditions, a battery of leaching tests was specifically designed to simulate various physical and chemical release mechanisms. 

Finally, there are many metal-containing solid wastes that may undergo leaching if disposed to land spent catalysts (cobalt, nickel, vanadium) spent batteries (nickel, cadmium, lithium, lead) combustion ashes etc. 

Nickel and cadmium are used in the production of NiFe rechargeable batteries. Using the AmMAR concept, the main leaching procedure to dissolve these valuable metals from spent accumulator scrap and production waste is performed in a two-step procedure, first with an ammonium carbonate solution and second with diluted sulfuric acid to obtain very high leaching efficiency (Fig. 14.18). 

Due to chemical passivation in old waste materials, subsequent leaching of the leach residue with sulfuric acid, with perhaps some oxidation, is necessary to achieve very high yields. If the pH is kept about 3 in this second treatment, leaching of iron is negligible. Also, to reduce iron in the leach solution, spent potassium hydroxide electrolyte from discarded batteries can be used for iron hydroxide precipitation. 

The hazardous components of MSW, ie, household chemicals, oily wastes, and lead and other metals in batteries, can leach from landfills and contaminate both surface water and groundwater or enter the atmosphere. Increased regulation to improve landfill integrity has led to impermeable liners and drainage and water quality monitoring systems. As a result, in many urban areas, land is either no longer readily available for new landfills or is available only at high cost. 

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