Aqueous Leaching Research Articles

Comprehensive Processing of Saline Aluminum-Containing Slag

A method is developed for processing saline aluminum-containing slag based on leaching and electrolysis of solid residue after leaching in molten fluoride with preparation of a deoxidizing alloy for steel. Saline solution is evaporated with preparation of a covering and/or covering-refining flux. In the course of pilot plant tests, optimum process conditions are clarified for aqueous leaching of saline aluminum-containing slag, and a test batch of alloy-deoxidizing agent is obtained that is used at the Electrostal Heavy Engineering Plant. The best results are achieved with the following leaching regime: temperature 60°C, size 150 μm, duration 80 min, and S:L = 2:1. Current efficiency 87%.

Released fraction of polychlorinated biphenyls from soil-biosolid system using a leaching procedure and its comparison with bioavailable fraction determined by wheat plant uptake.

The bioavailability of polychlorinated biphenyls (PCBs) in soils amended with biosolids was estimated using an aqueous leaching process of the compounds combined with rotating disk sorptive extraction (RDSE), and compared with bioavailability determined through of PCB absorption in wheat plants growing in the same soil-biosolid matrix. The matrices consisted of soil amended with biosolids at doses of 30, 90, and 200Mg/ha, which increase concomitantly the organic matter content of the matrix. Considering that PCBs were natively absent in both the biosolids and soil used, the compounds were spiked in the biosolids and aged for 10days. For each biosolid dose, the aqueous leaching profile was studied and equilibrium time was calculated to be 33h. The leaching fractions determined by RDSE, considering total PCBs studied, were 12, 7, and 6% and the bioavailable fractions absorbed by the wheat root were found to be 0.5, 0.3, and 0.2% for 30, 90, and 200Mg/ha doses, respectively. Both fractions leachable and bioavailable decrease with both increasing hydrophobicity of the compound (Kow) and increasing in the biosolid dose. It was found that both fractions (leaching and bioavailable) correlated according to the bivariate least squares regression, represented by a coefficient of correlation of 0.86. Therefore, the application of the chemical method involving a leaching procedure is an alternative to estimate the bioavailable fraction of PCBs in wheat plants in a simpler and in a shorter time.

The influence of ZnO incorporation on the aqueous leaching characteristics of a borosilicate glass

With increasing ZnO content, short term aqueous durability enhancement of all elements in borosilicate glasses containing 1.0 and 3.85 wt% ZnO was evident in 7-day PCT-B tests. In 14-day MCC-1 type leach tests conducted at 90 °C, surface alteration was very clear in the undoped glass via the formation of strongly altered amorphous material which tended to spall off the surface. No sign of crystallinity was detected by grazing incidence X-ray diffraction or electron microscopy of the surface layers and the surface material was very rich in silica. For the ZnO-bearing glasses, significant growth of particles following PCT leaching for 7 days was observed, due to a build-up of surface ZnO-containing Si-rich material and possible agglomeration. This alteration layer was also observed in MCC-1 type experiments in which cross-section SEM-EDS data were obtained. Raman, infrared and 11B and 29Si MAS NMR spectroscopy showed only slight changes in boron speciation on the addition of up to 9.1 wt% ZnO. Bulk positron annihilation lifetime spectra (PALS) of glasses containing 0–3.85 wt% ZnO could be analysed with three distinct lifetimes and also showed only slight differences. These results indicate that the basic glass structure was essentially not influenced by the ZnO content and that the passivation of the alteration layer is promoted by ZnO content.

Prediction of Acid Mine Drainage (AMD) and Metal Release Sources at the Küre Copper Mine Site, Kastamonu, NW Turkey

Waste and lithological rocks were subjected to aqueous leaching, acid base accounting (ABA), and net acid generation (NAG) tests, and detailed mineralogical investigations were conducted to predict acid mine drainage (AMD) formation at Turkey’s largest historical copper deposits. The field water chemistry from springs and seeps on the mine site were compared with the static and long term aqueous leaching test results. During the ABA, NAG and long term paste pH tests, ore rich and ore bearing wastes showed a paste pH <4, implying their acid generating nature. The relationship between net neutralization potential and acid producing potential revealed that waste rocks with a low sulfur content were generally low potential sources of AMD. Consistent with the static test results, aqueous leaching tests revealed that greater concentrations of Fe, Cu, Zn, Ni, Pb, Cd, Co and As were released from the wastes rich in pyrite. The test methods all generally agreed that the ore-rich wastes (O, P1C, P1D) were the main sources of AMD and metal contamination in the district.

Impact of iron and magnesium on glass alteration: Characterization of the secondary phases and determination of their solubility constants

In this study, the effects of iron and magnesium on International Simple Glass (ISG) alteration were studied throughout 511 days of aqueous leaching experiments. The aim was to determine by thorough characterization, the nature of the alteration products that control glass alteration. Iron and magnesium were added separately or together in solution as FeCl2 and MgCl2 salts, with monthly additions to compensate for their consumption. The alteration degree was determined by leachate analyses (ICP-AES) and the alteration products composition, morphology and microstructure were characterized (SEM, TEM-EDX and XRD).The results indicated that magnesium and iron increase glass alteration, forming tri-octahedral smectites with the same (Fe + Mg)/Si ratio. With iron, two kinds of silicates precipitate with the same composition but with a different morphology, whereas with magnesium alone, a single Mg-silicate forms. Moreover, it was found that the glass alteration rate drops when the pH stabilizes at a minimum value of 7.8 for Mg-silicates and 6.2 for Fe-silicates. At this point the secondary silicates stop precipitating. This result was confirmed by geochemical simulation and the solubility product of these silicates was estimated considering the presence or absence of aluminum in their structure.Finally, a two-step process was proposed to explain the location of the secondary phase precipitation: firstly in solution and at the solution/gel interface, and secondly in a highly porous upper zone of the gel.

Properties of chars from the gasification and pyrolysis of rice waste streams towards their valorisation as adsorbent materials

Rice straw (RS), rice husk (RH) and polyethylene (PE) were blended and submitted to gasification and pyrolysis processes. The chars obtained were submitted to textural, chemical, and ecotoxic characterisations, towards their possible valorisation.Gasification chars were mainly composed of ashes (73.4–89.8wt%), while pyrolysis chars were mainly composed of carbon (53.0–57.6wt%). Silicon (Si) was the major mineral element in all chars followed by alkaline and alkaline-earth metal species (AAEMs). In the pyrolysis chars, titanium (Ti) was also a major element, as the feedstock blends contained high fractions of PE which was the main source of Ti.Gasification chars showed higher surface areas (26.9–62.9m2g−1) and some microporosity, attributed to porous silica. On the contrary, pyrolysis chars did not present a porous matrix, mainly due to their high volatile matter content.The gasification bed char produced with 100% RH, at 850°C, with O2 as gasification agent, was selected for further characterization. This char presented the higher potential to be valorised as adsorbent material (higher surface area, higher content of metal cations with exchangeable capacity, and lowest concentrations of toxic heavy metals). The char was submitted to an aqueous leaching test to assess the mobility of chemical species and the ecotoxic level for V. fischeri.It was observed that metallic elements were significantly retained in the char, which was attributed mainly to its alkaline character. This alkaline condition promoted some ecotoxicity level on the char eluate that was eliminated after the pH correction.

Microstructure and performance studies of (Mo, Ru, Pd, Zr) tetra-doped gadolinium zirconate pyrochlore

ABSTRACTProper disposal of nuclear waste with multi-nuclides and multi-valence is still challenge. A series of (Mo, Ru, Pd, Zr) tetra-doped Gd2Zr2O7 ceramics were studied to understand the microstructure and performance evolution of nuclear waste forms that immobilised simulated waste after trialkyl phosphine oxides (TRPO) process. The structure of as-obtained samples were tested by X-ray diffraction, Raman, scanning electron microscope, electron back-scattered diffraction, and energy-dispersive X-ray spectroscopy, while the mechanical and chemical performance were characterised by Vickers hardness and aqueous leaching method. The results indicate that the mechanical behaviour are closely linked with the phase structure, and the highest Vickers hardness is obtained at the phase turning point. The leaching results show that the normalised leaching rate (LR) of the doped elements decrease in the order of Mo, Ru, Pd, Zr. After reaching equilibrium, their LR are as low as 4.12 × 10−4 g·m−2·d−1, 1.50 × 10−5 g·m−2·d−1, 1.30 × 10−5 g·m−2·d−1, and 2.09 × 10−7 g·m−2·d−1, respectively.

Acquisition of Anion Profiles and Diffusion Coefficients in the Opalinus Clay at the Mont Terri Rock Laboratory (Switzerland)

Chloride, bromide and sulphate concentration profiles have been analysed through the Opalinus Clay of Mont Terri in the framework of the Deep Borehole Experiment. Aqueous leaching and out diffusion experiments were carried out to acquire anion concentrations and estimate pore diffusion coefficients. Out diffusion technique gave consistent values of chloride and bromide compared to the concentration profiles acquired so far at the tunnel level of the Mont Terri rock laboratory. Concentrations acquired by leaching experiments show a maximum chloride concentration of 16.1 ± 1.7g/l at the basal part of Opalinus Clay which is higher than the value of 14.4 ± 1.4g/l obtained by out diffusion at the same level. This excess of chloride is likely due to dissolution of Cl− bearing minerals or release of Cl initially contained in unaccessible porosity. Bromide to chloride ratios are virtually the same as that of seawater, whereas sulphate to chloride ratios are significantly higher. Those latter are probably due to pyrite oxidation and dissolution of sulphate-bearing minerals occurring during sample collection and preparation. An anisotropy ratio of 2.4 was estimated for pore diffusion coefficient in the Opalinus Clay sandy facies.

A response surface analysis of the aqueous leaching of amylose from maize starch

A response surface analysis with a face centered central composite design was implemented to study the effect of maize (Zea mays L.) starch concentration (3.0–7.0% w/v) and leaching temperature (LT, 70–90 °C) on aqueous leaching of amylose (AM) as a way to optimize the conditions for obtaining the highest yield of long chain AM [number average degree of polymerization (DPn) ranging between 860 and 930] and highest purity. Second order empirical models were fitted via the least squares approach. Negligible terms were removed using backwards model reduction. Negligible lack of fit terms were obtained for the responses total leached carbohydrate and DPn. The optimization was complemented with a desirability test using the purity of the extracts. As targets for the optimization, maximum leachate yields, DPn ≈ 900, and purity >95% were set. The reported contour plots and prediction profilers can be used for tailor made production of leachates. Temperature had the most significant main effect as yields and DPn increased with temperature at the expense of purity. Purity was highly compromised when treatments were above 85 °C. This was reflected in the high DPn values (>1500) which suggested the presence of amylopectin material. When using 3.0% (w/v) maize starch suspension at an LT of 81 °C, the largest yield (15.0% of starch) of high DPn AM chains (DPn ∼ 900) and less than 3.3% of non-AM material were obtained.

Aqueous leaching of cattle manure incineration ash to produce a phosphate enriched fertilizer

Ash produced from the combustion of livestock manure contains large amounts of phosphorus (P), which is an important resource as a fertilizer. Some studies have extracted and recovered P from incinerated biomass ash using inorganic acid or alkaline agents, which produce wastewater that requires treatment and is expensive due to the cost of chemicals. Livestock manure ash contains not only P, but also water soluble salts, which could be a negative influence on plant growth and shall be preferably removed from the recovered fertilizer. In this study, we removed salinity from cattle manure incineration ash by simple aqueous leaching, while retaining the P content. The optimal condition was a 20 min leaching time at a liquid/solid (L/S) ratio of 10 mL g-ash−1. Under this condition, over 90 % of Cl and 20 % of Na in the original ash was removed, while over 99 % of the P was retained in the leached residue. The leached residue met the fertilizer standard in Japan in terms of citrate soluble fertilizer components and contained few heavy metals. X-ray analyses of the ash indicated that Cl was mainly present as KCl in the original ash, while P was mainly present as Ca compounds in the ash.

Influence of the starch structure in the synthesis and the yield of levulinic acid

Starch is a promising feedstock for the synthesis of chemical intermediates like levulinic acid (LA), but the role played by the amylose–amylopectin ratio of starch in LA yields has not been investigated so far. In this work, corn starch was fractionated using the aqueous leaching–alcohol precipitation method, and the morphological and thermal degradation characteristics of the amylose and amylopectin obtained were studied. A comparison of the results of acid-catalysed hydrolysis of the original starch and the fractions showed that differences in granule size, solubility, and susceptibility to acid hydrolysis are the main factors affecting LA yields. Amylopectin yielded LA at faster rates at 150 and 165°C than amylose, which is a factor that may influence the selection of starches for the production of LA at an industrial scale.

The extent of maize starch crystal melting as a critical factor in the isolation of amylose via aqueous leaching

Aqueous leaching from granular maize starch is a common technique for amylose (AM) isolation. Leaching was studied in a 60–90 °C temperature range. The leachate yield, degree of polymerization (DP) and purity were related to the extent of melting of the starch crystals at the leaching temperature as determined via differential scanning calorimetry. Annealing increases the amylopectin (AP) crystal stability and hence the remaining crystallinity at a given leaching temperature. Negligible AM leaching occurred at temperatures below the annealing dependent onset of melting. Leaching thus benefits from partial melting. Properties of AM leachates remained constant when the extent of starch melting remained below 80%. Loss of more than 95% of the melting enthalpy resulted in higher leachate DP at the expense of purity. As the crystallinity of annealed starches at a given leaching temperature was higher than for native starches, the leachate purity was higher. Although in no cases residual AP crystals remained at 90 °C, annealed starches yielded more pure AM extracts in higher yields than did native starch. More effective leaching in this case may be due to annealing-induced strengthened AP–AP interactions and AM disentanglement from AP.

Measurement of selenomethionine and selenocysteine in fish tissues using HPLC-ICP-MS

The extraction and measurement of selenomethionine (SeMet) and selenocysteine (SeCys) in fish muscle and liver tissues were evaluated. Preliminary experiments were undertaken with marine certified reference materials. NRCC TORT 1/2 Lobster hepatopancreas, NRCC DOLT 2/3; Dogfish liver and NIST 1566 a/b Oyster tissue were extracted using aqueous leaching, enzymatic hydrolysis and acid hydrolysis with ultrasound, microwave assisted heating and conventional heating using a hybridisation oven. High Se recoveries were obtained with the use of methanesulfonic acid as an extractant (89–92%); however, the low pH required for extraction is not compatible with most HPLC columns and dilution is required to analyse extracts that precluded the measurement of Se in samples from relatively uncontaminated environments. As well, Se species (SeMet and SeCys) degrade with the use of highly acidic extractants. Enzymatic hydrolysis with protease type XIV gave good recoveries (63–67%), but only SeMet was stable in the extract. As SeCys was not stable, a derivatisation step using iodoacetamide to form a stable carboxymethylated complex was used prior to enzymatic hydrolysis. Conventional heating at 37°C for 20h and microwave assisted heating at 45°C for 45min gave similar recoveries for CRMs but conventional heating gave slightly better recoveries for fish tissues.Two separate complementary methods were developed for the measurement of SeMet and SeCys in marine fish tissues; SeMet was measured after protease XIV hydrolysis and analysis using anion or cation exchange chromatography-ICPMS, while for the measurement of SeCys a carbamidomethylation derivatisation procedure prior to the protease hydrolysis was used and the separation of the species was carried out using size exclusion chromatography, followed by C8 ion-pair reversed-phase chromatography with ICPMS. Recoveries of SeMet and SeCys added to CRMs and fish tissues were 97±9% and 84±9% respectively.

On the removal of hexavalent chromium from a Class F fly ash

Coarse and fine samples of a Class F fly ash obtained from commercial combustion of Illinois bituminous coal have been exposed to two long-term leaching tests designed to simulate conditions in waste impoundments. ICP-AES analysis indicated that the coarse and fine fly ash samples contained 135 and 171mg/kg Cr, respectively. Measurements by XAFS spectroscopy showed that the ash samples originally contained 5 and 8% of the chromium, respectively, in the hexavalent oxidation state, Cr(VI). After exposure to water for more than four months, the percentage of chromium as Cr(VI) in the fly-ash decreased significantly for the coarse and fine fly-ash in both tests. Combining the XAFS data with ICP-AES data on the concentration of chromium in the leachates indicated that, after the nineteen-week-long, more aggressive, kinetic test on the coarse fly ash, approximately 60% of the Cr(VI) had been leached, 20% had been reduced to Cr(III) and retained in the ash, and 20% remained as Cr(VI) in the ash.In contrast, during the six-month-long baseline test, very little Cr was actually leached from either the coarse or the fine fly-ash (<0.1mg/kg); rather, about 66% and 20%, respectively, of the original Cr(VI) in the coarse and fine fly-ash was retained in the ash in that form, while the remainder, 34% and 80%, respectively, was reduced and retained in the ash as Cr(III). The results are interpreted as indicating that Cr(VI) present in Class F fly-ash can be reduced to Cr(III) when in contact with water and that such chemical reduction can compete with physical removal of Cr(VI) from the ash by aqueous leaching.

Pulsed electric discharge treatment of uranium leaching solutions: A method for accelerated extraction

Depletion of uranium ore deposits is leading to a need for more efficient uranium extraction techniques. In this study, gas-phase electric discharge is applied to an aqueous leaching solution dispersed between electrodes as a technique for enhancing acidic extraction of uranium. Application of the electric discharge treatment resulted in a 1.5 to 2.0 times increase in the leaching rate and an improvement in uranium recovery of 4%. The enhanced extraction method was found to involve oxidation of ferrous ions in the acidic aqueous solution by nitrogen-containing ions generated in the spark discharge channels.

Production of glutinous rice flour from broken rice via ultrasonic assisted extraction of amylose

In this study, a modified aqueous leaching method by complex formation of amylose with glycerol was employed for reducing the amylose content of starch in broken white rice to less than 2%, so that the resulting starch can be classified to that of glutinous rice flour. By employing ultrasonication in alkaline condition, extraction of amylose could be performed by washing at lower temperature in shorter time compared to the existing aqueous leaching method. The effects of glycerol concentration, alkali concentration, ultrasonication and treatment time on the amylose content of the treated starch were systematically investigated. Under optimum condition, amylose content of broken white rice starch can be reduced from 27.27% to 1.43% with a yield of 80.42%. The changes in the physicochemical properties of the rice flour before and after treatment were studied.

Multiphase simulation of mine waters and aqueous leaching processes

Managing of large amounts of water in mining and mineral processing sites remains a concern in both actively operated and closed mining areas. When the mining site with its metal or concentrate producing units is operational, the challenge is to find either ways for economical processing with maximum yields, while minimizing the environmental impact of the water usage and waste salt treatments. For safe closure of the site, the environmental control of possible drainage will be needed. For both challenges, the present-day multiphase process simulations tools can be used to provide improved accuracy and better economy in controlling the smooth and environmentally sound operation of the plant. One of the pioneering studies in using the multiphase thermodynamic software in simulation of hydrometallurgical processes was that of Koukkari et al. [1]. The study covered the use of Solgasmix equilibrium software for a number of practical acid digesters. The models were made for sulfuric acid treatments in titania pigment production and in NPK fertilizer manufacturing. During the past two decades the extensive data assessment has taken place particularly in geochemistry and a new versions of geochemical multiphase equilibrium software has been developed. On the other hand, there has been some progress in development of the process simulation software in all the aforementioned fields. Thus, the thermodynamic simulation has become a tool of great importance in development of hydrometallurgical processes. The presentation will cover three example cases of either true pilot or industrial systems including a South African acid mine water drainage treatment, hydrometallurgical extraction of rare earths from uranium leachate in Russia and a multistage process simulation of a Finnish heap leaching mine with its subsequent water treatment system.

Recycling of Electronic Waste, Using Basic and Acid Leaching

This recycling of printed circuit board (TCI) for the production of metals, given the environmental degradation that can cause toxic substances of these, is the reuse of valuable materials recovered from the TCI, this being an economic engine that promotes the recycling of this waste. This paper presents a methodology for evaluating the reaction kinetics and leaching of metals that form the metal substrate, which have environmental and energy advantages, so the generation of new recovery techniques metals from the TCI low environmental and energy impact is increasingly necessary, for it is essential to establish the parameters affecting the reaction rate and identify design alternatives to determine whether or not sustainable, economically viable and that does not pollute. The method adopted was a leaching acid samples, where the full factorial method employed two experimental levels to evaluate the influence of: leaching time, temperature of the aqueous leach solution, reaction kinetics and solid/liquid, on the percentage of metal extraction. Subsequently, the metals are obtained by calcining and smelting the resulting salts by addition of acid liquor.

Impact of Zn, Mg, Ni and Co elements on glass alteration: Additive effects

The minor elements present in the nuclear glass composition or coming from the groundwater of the future repository may impact glass alteration. In this study, the effects of Zn, Mg, Ni and Co on the International Simple Glass (ISG) alteration were studied throughout 511 days of aqueous leaching experiments. The aim was to determine their additive or competitive effect on glass alteration and the nature of the alteration products. The four elements were introduced separately or altogether in solution as XCl2 chloride salts (X = Zn, Mg, Ni or Co) with monthly additions to compensate for their consumption. The alteration kinetics were determined by leachate analyses (ICP-AES) and alteration products were characterized in terms of composition, morphology and microstructure (SEM, TEM-EDX, ToF-SIMS and XRD).Results indicate that when they are introduced separately, Zn, Mg, Ni and Co have the same qualitative and quantitative effect on glass alteration kinetics and on pH: they form secondary phases leading to a pH decrease and a significant increase in glass alteration. The secondary phases were identified as silicates of the added X element: trioctahedral smectites with a stoichiometry of[(Si(4-a) Ala) (X(3-b) Alb) O10 (OH)2](a+b)− [Xc Nad Cae] (2c+d+2e) + with a = 0.11 to 0.45, b = 0.00 to 0.29, c = 0, d = 0.19 to 0.74 and e = 0.10 to 0.14. . It was shown that as pH stabilizes at a minimum value, X-silicates no longer precipitate, thus leading to a significant drop in the glass alteration rate. This pH value depends on X and it has been identified as being 8 for Mg-silicates, probably around 7.3 for Ni and Co-silicates and less than 6.2 for Zn-silicates.When tested together, the effects of these four elements on glass alteration are additive and lead to the formation of a mix of X-silicates that precipitate as long as their constitutive elements are available and the pH is above their respective minimum value. This study brings new quantitative information about the effects of phyllosilicates precipitation on glass durability. These results are important since the precipitation of secondary phases could control, at least partially, the long-term behavior of nuclear glasses in geological repository conditions.

Leaching of Trace Elements from Indian Coal

Abstract Metal contamination due to coal leaching has caused various detrimental health hazards in the vicinity of mining industries. To evaluate the release of metal upon weathering under natural condition, aqueous leaching experiments of three different coal samples, from three coalfields - Neyveli, West Bokaro and Makum, were carried out. These coalfields represent three contrasting geological settings. Concentration of Cu and Cr in West Bokaro, and Ni in Makum coal exceeds that of world range. Leachate from Makum coal is highly acidic and contains very high concentration of Fe, Ni, Pb, Mn and Cd. This is mainly caused due to the dominance of pyrite in coal. On the other hand, coals from other mines release near neutral to slightly alkaline leachate. Leachate quality is mainly controlled by the mineralogy, which is a manifestation of depositional environment. Therefore, proper care needs to be taken during storage and dumping of coal at Makum area in order to control the metal contamination.