Slow Extraction Rate Research Articles

Bioleaching of metal polluted mine tailings aided by ultrasound irradiation pretreatment

Bioleaching of metal mine tailings is a well-known technology capable of recovering metals from these wastes in a sustainable way. Its major drawbacks are the relatively slow extraction rate and low efficiency, which usually imply long operating times. In this work it was assessed if the application of a pretreatment consisting in ultrasounds (US) irradiation could improve the rate and efficiency of the subsequent bioleaching process; additionally, it was also checked if US affects the activity of the acidophilic autochthonous microbial population present in the tailings. Bench-scale slurry phase batch experiments were performed in two steps: (1) US pretreatment and (2) bioleaching using a biostimulation strategy. Different frequencies (37 and 80 kHz) and energy dosages (0–18 kJ g−1) were used. The results obtained showed that the application of US had a positive impact in the process by increasing the leaching rate of all the metals studied (Fe, Al, Zn, Mn, and Cu). The effect of the US was more remarkable for a frequency of 80 than 37 kHz; in addition, a maximum of the bioleaching rate was obtained for an energy dosage in the range 10–15 kJ g−1. Specifically, bioleaching rates increased by 150, 95, 48, 38 and 28% for Zn, Al, Mn, Cu and Fe, respectively, due to the enhancement of the particle fragmentation and mass transfer rates caused by the US irradiation. However, it must be taken into account that high energy dosages could have a detrimental effect over the microorganism’s population, slowing down the overall process of metal leaching.

New Concept for the Study of the Fluid Dynamics of Lithium Extraction Using Calix[4]arene Derivatives in T-Type Microreactor Systems

Lithium extraction remains a challenge in the hydrometallurgy process due to its economic value and maldistribution sources. Employing calix[4]arene derivatives in solvent extraction techniques results in high selectivity and extraction capability, but a slow extraction rate. The slow kinetics of batch-wise extraction can be drastically accelerated by using a T-type microreactor system. Therefore, a combination of calix[4]arene and a microreactor system serves as an ideal platform for efficient lithium extraction. In this work, the fluid dynamics of lithium extraction using a monoacetic acid calix[4]arene derivative in a T-type microreactor system were studied. Increasing the O/A ratio increases the average length, surface area, and volume of the organic droplets, but decreases the specific surface area. In contrast, increasing the Reynolds number decreases the average length, surface area, and volume of the organic droplets, but increases the specific surface area. It was found that shorter diffusion distance, larger specific surface area, and faster vortex velocity were the factors that play the most pivotal roles in achieving great extraction rate enhancement in T-type microreactor systems compared to batch-wise systems. These findings represent an important new concept in the study of the fluid dynamics of lithium extraction using monoacetic acid calix[4]arene derivatives in T-type microreactor systems.

Separation of Aluminum and Iron from Lanthanum—A Comparative Study of Solvent Extraction and Hydrolysis-Precipitation

This study investigates the removal of aluminum and iron from rare earth element (REE) containing solutions by solvent extraction with saponified naphthenic acid and by hydrolysis-precipitation. The results emphasize both, the preferential application as well as limitations of every method. We find that emulsification occurring during the solvent extraction of aluminum is caused by its slow extraction rate in comparison to the neutralization reaction and by the proximity of the pH value required for aluminum extraction and the pH value at which hydrolysis of aluminum occurs. However, by choosing a long shaking time of at least 4 h, the emulsion recedes. The formation of emulsion can be avoided by strict control of pH value during the extraction. Moreover, the loading capacity of the organic phase with aluminum is limited due to the strong increase in viscosity of the organic phase with increasing aluminum concentration and due to the gel formation. Regarding the extraction of iron, the amount of extracted ions is limited due to the overlap of the pH range required for the extraction with pH range in which sparingly soluble iron oxides/hydroxides are formed. In summary, aluminum and iron can be simultaneously removed from REE-sulfate solution by solvent extraction with saponified naphthenic acid in one extraction stage only from diluted solutions. However, in comparison to the hydrolysis-precipitation method, a higher purity of the solution is achieved. A complete removal of aluminum and iron from concentrated solutions can be achieved in two stages. First, the content of aluminum and iron should be reduced by hydrolysis-precipitation. After that, a high-purity solution can be obtained by subsequent solvent extraction by saponified naphthenic acid.

The acidic ferric sulfate leaching of primary copper sulfides under recycle solution conditions observed in heap leaching. Part 1. Effect of standard conditions

Understanding the dissolution of copper from chalcopyrite is important as chalcopyrite is the most abundant copper mineral in the earth's crust. The main method for extraction of copper from chalcopyrite is by flotation concentration before being smelted and electro-refined. However, this process is not suitable for the treatment of the vast reserves of low grade chalcopyrite ores, where hydrometallurgical extraction through heap leaching is a better option. While pressure or high temperature leaching with the addition of sodium chloride or HCl have been proposed to extract copper from chalcopyrite concentrates, this process is too expensive to treat low grade copper ores. Currently the research focus to develop a treatment process involves the use of bacteria to oxidise the sulfide minerals and produce sulfuric acid. Given the slow extraction rates of this process it requires decades to extract all the copper from the mineral which would mean the leach solution would therefore be recycled during the process once the copper had been removed. While previous studies have reported the effect of leach temperature, pH (acid concentration) and Eh on copper extraction, these have only considered initial leaching conditions. Studies using recycle leach solution conditions have not been undertaken, and this is the focus of the study reported here. The recycle solution conditions were based on a simulated long term solution composition. This article is part of a series of papers that has investigated the effect on copper and iron extraction from chalcopyrite which has evaluated conditions, major species and additives under recycle leach concentrations. This article examines the effect of the conditions, specifically temperature, pH, Eh and solids density. It was determined that the temperature had the most significant effect on the copper and iron extraction while the pH, Eh or solids density had no appreciable effect on the extraction of either copper or iron under the recycle leach conditions tested. While the effect of temperature on chalcopyrite dissolution is known, the activation energy, the rate of dissolution and the degree of copper extraction is lower under these high solute or recycle concentrations. Similar observations were found when studying pyrite but this study attributed the lowering of these parameters under recycle conditions to the sulfate concentration causing a diffusion layer around the mineral particles which alters or slows the response of pH, Eh or temperature on the dissolution reaction.

Polarimetry concept based on heavy crystal hadron calorimeter

In the ongoing JEDI (Jülich Electric Dipole moment Investigations) project, the essential point will be to measure a tiny beam polarization change over an extended period of time. The particle scarcity in the polarized deuteron or proton beams and the required slow extraction rate puts tough experimental constrains on the polarimetry. For the EDM measurements, a dedicated high precision polarimeter is required. To fulfill specifications, a fast, dense, high resolution (energy and time), and radioactive hard novel crystal scintillating material is required. LYSO crystals are supposed to be used as an ideal scintillating material for this kind of detector. The LYSO crystal PMT and SiPM readout, with a FADC based system is under development. The first proton and deuteron beam test of the prototypes are presented here. In this paper, the new polarimetry concept and preliminary results from first proton and deuteron beam time are presented.

CO2 extraction from seawater using bipolar membrane electrodialysis

An efficient method for extracting the dissolved CO2 in the oceans would effectively enable the separation of CO2 from the atmosphere without the need to process large volumes of air, and could provide a key step in the synthesis of renewable, carbon-neutral liquid fuels. While the extraction of CO2 from seawater has been previously demonstrated, many challenges remain, including slow extraction rates and poor CO2 selectivity, among others. Here we describe a novel solution to these challenges – efficient CO2 extraction from seawater using bipolar membrane electrodialysis (BPMED). We characterize the performance of a custom designed and built CO2-from-seawater prototype, demonstrating the ability to extract 59% of the total dissolved inorganic carbon from seawater as CO2 gas with an electrochemical energy consumption of 242 kJ mol−1(CO2).

Unusually Slow Extraction Rate and Mechanism of Iron(III) with Trifluoroacetylacetone in Triton X-100 Micellar System. Part II. Interfacial Transport

In order to learn reasons of the slow formation/extraction rate of iron(III) with trifluoroacetylacetone in Triton X-100 micellar system, the rate of material transport of the extractable tris-complex from the bulk aqueous phase to the micellar pseudophase was investigated at 298 K. The rate was successfully measured using a micellar-concentration-jump stopped-flow technique; the rate was independent of the ligand, the hydrogen ion and the Triton X-100 concentrations of the starting solutions while it was first order with respect to the surfactant concentration of the resulting solutions. The rate of transport was slow enough to reduce the rates of the overall extraction reactions. The rate of formation/extraction in the micellar system was recalculated as if the extraction of the tris-complex was negligibly slow; the corrected rate constant agreed well with that obtained in the aqueous solution. The slow extraction rate observed in the trifluoroacetylacetone-Triton X-100 micellar system was concluded to be due to the slow interfacial transport of the tris-complex.

Unusually Slow Extraction Rate and Mechanism of Iron(III) with Trifluoroacetylacetone in Triton X-100 Micellar System. Part I. Extraction Routes

The rate of formation/extraction of iron(III) with trifluoroacetylacetone in Triton X-100 micellar solution at 298 K was measured by stopped-flow spectrophotometry to identify the route and mechanism of the extraction process. The rate was first order with respect to the metal ion and the extractant in the bulk aqueous phase and inverse first order to the hydrogen ion when the formation of extractable tris-complex was small. The rate obtained under such conditions agreed well with that of complex formation in the single aqueous solution; this suggests that the whole reactions is controlled only by the formation of the mono-complex in the bulk aqueous phase. On the other hand, the rate did not show clear dependencies on the ligand and the hydrogen ion, and was slower than the one expected from the complex formation in the aqueous solution when the formation of the extractable tris-complex was dominant. A slow material transport of the tris-complex from the bulk aqueous phase to the micellar pseudophase was estimated.

Liquid–liquid extraction of platinum(II) with cyclic tetrathioethers

The liquid–liquid extraction of platinum(II) with 12-, 14- and 16-membered cyclic tetrathioethers from chloride solution was studied. Bromocresol Green ion as a counter anion and 1,2-dichloroethane as an extraction solvent were used. The effect of thiourea on the extraction rate of platinum(II) was examined. Platinum(II) was hardly extracted with macrocyclic tetrathioethers in the absence of thiourea because of the slow extraction rate. The extraction rate of platinum(II) was considerably enhanced by the addition of thiourea. The extraction rate of platinum(II) with 16-membered cyclic tetrathioether was faster than that with 12- and 14-membered ones. Platinum(II) was quantitatively extracted with 16-membered cyclic tetrathioether into 1,2-dichloroethane within 5 h in the presence of thiourea.

Regeneration of Five Activated Carbons with Methanol

The regeneration characteristics of five commercially available granular activated carbons with methanol were evaluated. Three of the adsorbents were bituminous base carbons, while the remaining two were manufactured from lignite coal and wood. The adsorbates were p-chlorophenol, and two-ring, four-ring and eight-ring azo dyes. The rate of regeneration of the five adsorbents appeared to be sensitive to the molecular weight of the adsorbate; decreasing with increasing molecular weight. During the methanol regeneration of the p-chlorophenol and two-ring dye, an upper limit for capacity recovery was observed for all adsorbents, suggesting that a maximum recoverable capacity has been obtained. This phenomenon was not observed for the remaining two adsorbates due to exceedingly slow extraction rates. The extraction efficiences obtained for p-chlorophenol and the two-ring dye were found to correlate with the adsorption energies of these adsorbates on activated carbon. The extraction efficiency was observed to decreased with increasing adsorption energy.