Batch extraction experiments

Conceptually, the solvent extraction process involves contacting the contaminated sludge with a solvent so that some of the PCB sorbed on the sludge will be desorbed. At long contacting times an equilibrium partitioning of the PCB between the sludge and the solvent phases (henceforth desorption equilibrium) will be obtained. Batch extraction experiments were performed to establish the equilibrium desorption charasteristics. 

From a process design standpoint, it would be desirable to contact the solvent and sludge for as short a time as possible, using as little solvent as possible, in order to minimize the capital and operating costs of the process. Batch extraction experiments were performed to establish the characteristics time for attaining desorption equilibrium. 

A straightforward, though not optimal, solvent extraction process design would involve repetitive contacting of the sludge with fresh solvent until satisfactory cleanup has been achived. The feasibility of such a design can be easily verified through consecutive batch extraction experiments, and these experiments were also performed. 

In order to determine the characteristic time for the desorption of PCB from the sludge into the solvent physe, and the desorption equilibrium behavior, batch extraction experiments were carried out in 2 oz. glass bottles equipped with teflon septum insert caps. Variable amounts of dried sludge were contacted with 20 mL of solvent at room temperature. Magnetically stirred, teflon-coated bars facilitated mixing of the solvent and the sludge. 

Thermodynamic calculations and batch extraction tests showed that the Np(IV)-Pu(IV) and Np(VI)-Pu(VI) systems are unstable for solution concentrations practical for solvent extraction. Products of radiolysis provide a mechanism for oxidation of Np(IV) and reduction of Np(VI) and Pu(VI). Batch extraction experiments showed that the reaction rates of destabilizing reactions are fast enough that the systems cannot be stabilized for a practicable time for plant processing (8). 

Batch Extraction Experiments. A series of batch extractions was conducted in which water, NTA, and EDTA were used as the extractive agents. The initial lead concentrations on the soil were nominally 5(X), 1,000, 5,0(X), and 10,(XX) mg/kg soil after spiking the soil with the lead nitrate solution and allowing the samples to age at least six weeks. The concentrations of EDTA and NTA ranged from 0.01 to 0.10 M. Tl extractions were perfOTmed over the nominal pH range of 4 to 12. 

The effect of a continuous extraction will be demonstrated by the extraction of heavy hydrocarbon contaminants from soil by supercritical water. The suitability of supercritical water for extracting heavy hydrocarbons from soil material was shown previously by semi-batch extraction experiments [5]. At operating conditions of 653 K and 25 MPa extraction results of hydrocarbons from soil material are excellent, even if it is weathered for more than 20 years, but extraction times are long. In order to shorten clean-up times the extraction process has to be operated continuously. 

Batch Extractions. In nearly all commercial scale operations, a continuous extraction process, either mixer-settlers or colunm units, would be used. However, batch extraction experiments are useful for assessing overall feasibility and for optimizing the many process variables such as emulsion formulation and volume ratios of the internal, membrane, and external phases. Consequently, the most common experiment in this study was the batch extraction. In these experiments, 500 ml of a selenium solution (1 mg/L) were prepared in the extraction vessel, either in the presence or absence of other competing anions. The prepared emulsion (50 ml) was added and the mixture was stirred at a speed of 150 rpm. In this manner the emulsion drops were uniformly dispersed in the external phase while extraction proceeded. Samples of the external aqueous phase were taken at appropriate intervals and the concentrations of Se(IV), Se(VI), and sulfate were determined. 

Batch ELM Extraction of Selenium. A series of batch extraction experiments were carried out to assess the feasibility of an ELM process for the removal of selenium from refinery wastewater streams. To do this we developed emulsion formulations and evaluated these formulations for the capability of reducing the aqueous phase selenium concentration below 0.05 mg/L. Next, we carried out experiments to evaluate the effect of competition between the two oxidation states, the effect of total selenium concentration of the extraction behavior, the effect of external phase pH on the transport rate, and the effect of competing anions (like sulfate) on the extraction efficiency and kinetics. 

The results of the batch extraction experiments are presented in Figure 7, which is a plot of selenium concentration (either selenate or selenite) as a function of time during batch ELM experiments. It is clear that, in the absence of competing anions, both selenate and selenite... 

Competition Between Se(IV) and Se(VI) in the ELM Extraction of Selenium. A series of batch extractions were carried out to evaluate the competition between the two oxidation states of selenium, Se(IV) and Se(VI). In one set of batch extraction experiments we examined the extraction behavior of selenate [Se(VI)] in isolation (at 1 mg/L) and in the presence of an equal amount of selenite [Se(IV)]. In another set of experiments we studied the extraction behavior of selenite in isolation (at 1 mg/L) and in the presence of an equal amount of selenate. 

It was desired to determine if the extraction behavior of Se(IV) depends on the total selenium concentration in the external phase. To investigate the effect of external phase concentration on the rate of Se(IV) extraction, we carried out batch extraction experiments at two different initial concentrations (1 and 10 mg/L). The emulsion formulation was the same as described previously. The results are given in Figure 10 (a plot of Se(IV) concentration as a function of extraction time) and show that there is little difference in the initial extraction rates between 1 and 10 mg/L selenite. Beyond two minutes, the extraction rate of the higher amount (10 mg/L) tapers off. 

In simple experiments, particulate silica-supported CSPs having various cin-chonan carbamate selectors immobilized to the surface were employed in an enantioselective liquid-solid batch extraction process for the enantioselective enrichment of the weak binding enantiomer of amino acid derivatives in the liquid phase (methanol-0.1M ammonium acetate buffer pH 6) and the stronger binding enantiomer in the solid phase [64]. For example, when a CSP with the 6>-9-(tcrt-butylcarbamoyl)-6 -neopentoxy-cinchonidine selector was employed at an about 10-fold molar excess as related to the DNB-Leu selectand which was dissolved as a racemate in the liquid phase specified earlier, an enantiomeric excess of 89% could be measured in the supernatant after a single extraction step (i.e., a single equilibration step). This corresponds to an enantioselectivity factor of 17.7 (a-value in HPLC amounted to 31.7). Such a batch extraction method could serve as enrichment technique in hybrid processes such as in combination with, for example, crystallization. In the presented study, it was however used for screening of the enantiomer separation power of a series of CSPs. 

Table II. Recovery for CLLE and Batch Extraction at pH 3 with and without Humic Material Experiment 2...

Figure 5. Linear regression analysis of 1-L batch versus 1-L continuous liquid-liquid extraction Experiment 2.

Experiments were made using the solutions which contain 15-75 % (v/v) ethanol in the batch extraction system at 313 K and 120 atmospheres, for 60 minutes. Those experimental conditions were chosen because of the density of SC CO2 is near to the normal liquid density at these conditions and consequently it has a high solvent power [2], Experimental results were given at Table 1. 

Experiments were made using a solution which contains 60 %(v/v) ethanol in the batch extraction system in the pressure range of 80-160 atmospheres and at the temperatures of 313 and 333 K for 60 minutes. Experimental results were given in Table 2. As can be seen, extraction yield raised from 25 g/1 to 46 g/1, when temperature decreased from 333 K to 313 K at 80 atmosphere. Similarly, decreasing temperature increased the extraction yield both at 120 and 160 atmospheres. At 313 K, extraction yield raised from 46 g/1 to 60 g/1 with increasing pressure from 80 to 160 atmosphere. At 333 K, the effect of pressure was not as obvious. 

Because of the favorable sorptive properties of the reversed-phase supports, batch adsorption and desorption can be a very effective way to desalt a chromatographed sample or to partially fractionate a peptide mixture during a purification procedure. For example, 1-2 gm of an oc-tadecyl silica packed into a silanized glass or plastic pipette can be used for the batch fractionation of small amounts of a crude peptide extract from tissues, such as the pancreas or pituitary, or from a synthetic experiment. A number of commercial products, such as the Waters Sep-Pak, have found use in this manner 10) as a purification or sample preparation aid. Protocols for batch extraction procedures on alkyl silicas have been discussed 17a,b) and applied to neuropeptides 10, 158, 166) and other hormonal peptides 88, 162, 167, 168). With these methods recoveries of peptides present in a tissue extract are generally higher than those found with classical fractionation techniques due in part to the fact that proteolytic degradation is minimized. 

Fully active laboratory scale experiments were started using firstly a Windscale HAW solution (5000 l/t) generated by the reprocessing of Magnox fuel elements with a burn-up value of 3500 MWd/t. The overall decay time was about 10 months and as the composition was not known, only relative activity measurements were performed. Other fully active HAW solutions were subsequently prepared in Ispra hot cells by dissolving U02 samples irradiated at 26 — 36,000 MWd/t and cooled for about 4 years. Successive TBP batch-extraction steps were carried out under the 1st extraction cycle conditions of the Purex process to remove the bulk of U and Pu. 

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