Leaching batch extraction

A test method for the batch extraction of treated or untreated solid waste or sludge, or solidified waste, to provide an indication of the leaching potential (ASTM D-5233) is also available. The goal of this test method is to provide an extract for measurement of the concentration of various analytes and therefore may be applied to a study of the smaller molecules that reside within the coal matrix. This test method, as written, is intended to provide an extract suitable for measurement of the concentration of analytes that will not volatilize under the conditions of the test method and may appear to offer limitations on the use of coal, but the test method does describe a procedure for performing a batch extraction of a solid. Again, the sampling and handling requirements that may be associated with the analysis of coal should also be applied to the method. 

Batch extraction of the particle fractions were performed using the U.S. EPA EP-toxicity test and a modified version developed in our laboratories. The 2 main differences in these tests are 1) the EP-toxicity test uses 0.5 N acetic acid to enhance leaching whereas the modified test uses 17.4 N glacial acetic acid and 2) the EP-toxicity test limits the amount of acid added to keep the pH at 5.0 + 0.5 to 40 ml so that the actual pH of the leaching medium may be well above pH 5.0 if additional acid is needed, whereas there was no limit as to how much 17.4 N acetic acid could be added to keep the pH at 5.0 + 0.5 in the modified test. The samples were placed on a shaker-table in a controlled temperature room (20 C) the pH was monitored and adjusted over a 24 hour period as specified in the EP-toxicity test procedure[ 9 ]. 

Fig. 2. Calcium leached during sequential batch extractions of solidified/stabilized hazardous wastes...

Chelators such as EDTA, nitrilotriacetic acid (NTA), 1,2-aminocyclohexane 7V,7V,7V ,N7-tetraacetic (DCyTA), and ethylene glycol-bis(2-aminoethyl)-(V,(V, 7V ,7V -tetraacetic acid (EGTA) have been studied extensively and are well summarized (Peters, 1999). Chelator concentration and reaction pH influence metal complexation and the success of removal from soils. Sun et al. (2001) observed that batch extraction methods result in 1 1 molar extraction ratios of EDTA/metal (Pb, Cd, Zn, Cu) and reveal which metal is more or less soluble in EDTA solutions. Column leaching studies, however, relate the elution patterns and recalcitrance of the metals to desorption and dissolution by EDTA. There is concern over the detrimental effects on soil quality from using chelators because of their biotoxicity, persistence in soil environment, and their removal of beneficial micro-and macronutrients, which leave the washed soil infertile for revegetation when it is backfilled. 

D13. Batch leaching will be similar to a batch extraction, and the equations developed in Section 13.6 can be adapted when the solution is dilute or there is an insoluble solid matrix. We have 12.5 liters of pure water that we will use to leach 10.0 liter of wet sugar cane solids. Equilibrium data... 

Batch Extraction Chapter 7 presents the batch extraction operation. There are two types of extraction. Solid extraction or leaching involves solids which are leached or extracted by solvent where solubility of solids is the important property used for separation, and liquid extraction where immiscible solvent is used to extract liquid product from the mixture using liquid-liquid equilibria. 

There are two types of extraction processes, namely, leaching where solids are extracted and liquid-liquid extraction. The commonly used leaching equipment is the extraction battery where counter current flow is established resulting in a number of extracting stages. This can be modeled as equilibrium process. The McCabe-Thiele procedure can be used to model this process. In liquid-liquid extraction, ternary diagrams and tie lines are used to determine the extent of extraction. Batch extractive distillation is a commonly used extractive method for liquid-liquid extraction. 

Solvent Extraction. Solvent extraction has widespread appHcation for uranium recovery from ores. In contrast to ion exchange, which is a batch process, solvent extraction can be operated in a continuous countercurrent-fiow manner. However, solvent extraction has a large disadvantage, owing to incomplete phase separation because of solubihty and the formation of emulsions. These effects, as well as solvent losses, result in financial losses and a potential pollution problem inherent in the disposal of spent leach solutions. For leach solutions with a concentration greater than 1 g U/L, solvent extraction is preferred. For low grade solutions with <1 g U/L and carbonate leach solutions, ion exchange is preferred (23). Solvent extraction has not proven economically useful for carbonate solutions. 

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. 

The leached solids must be separated from the extract by settling and decantation or by external filters, centrifuges, or thickeners, all of which are treated elsewhere in Sec. 18. The difficulty of solids-extract separation and the fact that a batch stirred tank provides only a single equilibrium stage are its major disadvantages. 

The behavior of elements (toxicity, bioavailability, and distribution) in the environment depends strongly on their chemical forms and type of binding and cannot be reliably predicted on the basis of the total concentration. In order to assess the mobility and reactivity of heavy metal (HM) species in solid samples (soils and sediments), batch sequential extraction procedures are used. HM are fractionated into operationally defined forms under the action of selective leaching reagents. 

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