Leaching Solution Research Articles

The permeability evolution mechanism of ore-bearing strata during acid in-situ leaching of uranium: A case study of Bayanwula uranium mine in Inner Mongolia of China

Uranium mainly comes from ISL of sandstone-type uranium deposits in China. The change of porosity and permeability caused by blockage of ore-bearing strata is one of the most serious problems in acid ISL of uranium. In this paper, the groundwater tracer test was carried out before and 1 year after ISL to explore the pore and permeability evolution characteristics of the ore-bearing layer during ISL. The test results showed that the leaching solution migrated along two seepage channels and the water-bearing medium was isotropic. After 1 year of ISL, the flow rate of the leaching solution decreased obviously. However, the flow rate of the leaching solution in slower channel decreased more than that in the faster channel in all directions, which was caused by the more adequate chemical reactions between the leaching solution and the minerals of the ore-bearing layer and the more corresponding precipitation in the slower channel. In addition, the flow rate along the direction of groundwater flow decreased less than that in the direction of vertical groundwater flow. This was closely related to the transformation of aquifer medium by hydrodynamic field. Initial stage of ISL, the occurrence of plugging is closely related to the precipitation-dissolution process of iron and aluminum minerals under the change of pH, which is accompanied by the continuous precipitation of gypsum.

Molecular recognition on the surface of concentrated hydrochloric acid: Hydration configuration-driven preferential recognition of Rh (III) anions with inner-coordinated water molecules

Comprehension of selective recognition of anions is confined to a phenomenological list of solvents, hardly surpassing Pedersen’s empirical observations of cationic-crown ether binding. In this work, a novel strategy employing thin-layer oil membrane extraction (TOMX) on the surface of concentrated hydrochloric acid is proposed for controllable recognition and separation of anions with different hydration configurations. Four typical chloric-complexing anions, RhCl63−, PdCl42−, PtCl62− and FeCl4−, usually coexisting in the concentrated hydrochloric acid leaching solutions of precious metal concentrates were focused. A surprising phenomenon was noticed that the octahedral RhCl5(H2O)2− anions with inner-coordinated water molecules were preferentially recognized by 18C6 macrocyclic molecule. However, the planar quadrilateral Pd (II) chloric-complexing anions with a hydration configuration via water molecules attacking the central Pd (II) atoms along the Z-axis direction can be separated subsequently. The Pt (IV) and Fe (III) chloric-complexing anions respectively with an octahedral and tetrahedral outer-coordinated hydration shell configuration were the last to be recognized. Such an order in extracting Rh (III) > Pd (II) > Pt (IV) > Fe (III) anions depends on their hydration capacity and the preferential affinity towards the interface, which is almost impossible during the conventional stirring and oil droplet dispersed extraction. Because of a lower concentration of dissociated hydrogen ions on the surface of concentrated hydrochloric acid compared to its bulk concentrations, the hydration of those chloric-complexing anions was enhanced. The Rh (III) anions with inner-coordinated water molecules exhibit a higher interfacial affinity than other anions. The water molecules entering the inner coordination layer of Rh (III) chloric-complexing anions, cooperating with its outer-coordinated hydration shell, act as a hydrogen bond “water bridge” to interact with 18C6 molecules, which makes it easier to feel the influence from the aqueous laminar shear flow under the thin-layer oil membrane, thereby driving the preferential recognition of easily hydrated Rh (III) anions at the interface. The controllable “water bridge” interactions driven by shear flow can be activated or deactivated on the surface of concentrated hydrochloric acid by adjusting the shear flow rate. This work lays a foundation for the future development of a controllable flexible molecular recognition technology at liquid–liquid interfaces.

A new extraction mechanism in sulfuric acid media for the recovery of aluminum

The separation of aluminum and manganese from mineral leach solutions has been a challenge at present and has attracted great interest. In this paper, the effects of different extractants on aluminum recovery as well as the effects of the concentration of the most suitable extractant, extraction temperature, initial pH and organic phase/aqueous phase ratio on the recovery of aluminum were investigated. The results showed that for chromite recovery solution(CRS) with an initial aluminum concentration of 0.1221 g/L, S-NA at 0.25 mol/L exhibited good selectivity and extraction efficiency for aluminum, and was able to separate aluminum from other elements and recover it easily for secondary use without scrubbing. The extraction mechanism of aluminum in sulfuric acid medium was investigated through various analyses including the combination of energy and bond length calculations, electrostatic potential (ESP) theory calculations, IGMH analysis, process chemistry analysis, and thermodynamic equilibrium species calculations. These analyses showed that Al(III) was distributed in the recycling solution in the form of AlSO4+ and had strong interactions with naphthenate ions, and that the combination of AlSO4+ with the naphthenate ions(R−)’s formed the stable complex molecule AlSO4R. The study provides a feasible path for the recovery of aluminum in CRS and is of guiding significance for the theoretical study of aluminum in sulfuric acid media.

Selective extraction of germanium from iron-bearing ammonia leaching residue via low-temperature molten NaOH leaching

To address the insolubility of x(SiO2)·GeO2 and y(Fe3O4)·GeO2, this study introduced a two-step leaching (NaOH leaching-NL and low-temperature molten NaOH leaching- LTMNL) method. During the NL process, 51.30 % of germanium (Ge), 84.96 % of aluminum (Al), and 56.45 % of silicon (Si) were leached. Moreover, in the LTMNL process, over 97.43 % of Ge and nearly all amphoteric metals (e.g., Al, Zn, and As) were dissolved under optimized conditions (including a NaNO3-to-ore mass ratio of 0.15, leaching temperature of 170 °C, alkali-to-ore mass ratio of 10, agitation speed of 500 rpm, and reaction time of 2 h). The leachate obtained from the LTMNL process was used as a lixiviant in the NL process to facilitate the recyclable utilization of NaOH and enrich Ge in the leachate solution. This approach resulted in an overall germanium recovery efficiency of 98.72 %. The germanium concentration in the NL leachate exceeded 400 mg/L, thereby facilitating subsequent germanium recovery. Additionally, the LTMNL residue, containing an iron concentration of 52.46 wt%, served as an iron resource. Therefore, the two-step leaching process achieved high germanium recovery and efficient separation of Ge and Fe compared with conventional H2SO4 leaching methods. This indicates that the two-step leaching process is a promising and efficient method for treating germanium-bearing material in the form of x(SiO2)·GeO2 and y(Fe3O4)·GeO2).

Selective separation of rhenium from oxygen-pressure leach solution of molybdenite concentrate using modified D201 resin: Experiments and theoretical calculations

Recovering rhenium from highly acidic rhenium-containing leach solutions is challenging for most resins, particularly in multiplexed systems. Herein, we introduce a scheme for selectively obtaining rhenium from a multielement solution containing high concentrations of sulfuric acid using modified D201 resin. Considering the dosage of resin and parameters such as pH and adsorption temperature, the adsorption efficiencies under optimal conditions for rhenium, molybdenum, iron, and cerium were 97.46 %, 0.38 %, 0.94 %, and 1.10 %, respectively. The selective recovery mechanism of rhenium was investigated by fitting the experimental data to kinetic and adsorption isotherm models. The pseudo-second-order and Langmuir models better fit results corresponding to the experimental data, which indicates monolayer chemisorption of ReO4− formed on the resin surface. Meanwhile, various characterizations such as SEM-EDS, FTIR, XPS, etc., indicate that ReO4− initially combines with the protonated −CHN+H2CH2Cl on the modified resin surface and then undergoes ion exchange reaction with doped Cl−. Furthermore, because of the diverse forms and similar properties of molybdenum and rhenium ions in acidic solutions, a theoretical model based on density functional theory was used to simulate the selective adsorption process in leach solution with a pH of 1.7. The simulation results demonstrate a highest occupied molecular orbital–lowest unoccupied molecular orbital energy gap, observed in the following order: ΔEMoO22+ = ΔEReO4− < ΔEMoO42− < ΔEMo7O246−, which implies that MoO22+ and ReO4− were most likely to transition from their ground states to excited states and react with the electron donor and acceptor groups, respectively. Compared with MoO42−, ReO4− is more likely to react with the electron acceptor group and provides the corresponding methods and a theoretical reference for selective separation of rhenium in multielement solutions.

Ionic liquids functionalized chitosan: An effective, rapid and green adsorbent for gold recovery

Thiosulfate has been considered as a more environmentally-friendly alternative to cyanide salts for the extraction of gold from gold ores and the development of affordable, green and efficient adsorbents for the isolation of gold-thiosulfate complex (Au(S2O3)23−) from the leaching solution remains a significant challenge. To address this issue, chitosan, a natural macromolecule, was selected as a carrier and chemically modified with ionic liquids. The ionic liquids modified chitosan showed greater adsorption capacity towards Au(S2O3)23− compared with pristine chitosan. The adsorption of Au(S2O3)23− on ionic liquid modified chitosan followed Freundlich isotherm and pseudo-second order kinetic models, involving an anion-exchange mechanism with liquid film diffusion as the rate-limiting step. The chitosan modified with butylimidazolium-based ionic liquid had an adsorption capacity of 5.0 mg g−1 for gold (10 mg L−1 of gold, pH 6, 2 g L−1 of adsorbent dosage), outperforming other reported adsorbents. The ionic liquid modified chitosan showed a high adsorption efficiency of up to 96.7 % for Au(S2O3)23− in an actual thiosulfate leaching solution with a desorption efficiency of 98.4 %, suggesting that the ionic liquid modified chitosan has the potential to be a eco-friendly, biocompatible and effective adsorbent for the recovery of Au(S2O3)23−.

Solution circulation for green and sustainable gold extraction with an integrated low potential thiosulfate leaching-resin adsorption recovery process

A systematic research of solution circulation for gold extraction from a gold ore with an integrated low potential thiosulfate leaching-resin adsorption recovery process was performed by using the analysis and detection methods of ICP-OES, SEM-EDS, HPLC, XPS, etc. The pulp potential was controlled at about 200 mV under low reagent concentration and closed condition where the gold leaching percentage achieved 89.02 % while the thiosulfate consumption was only 19.22 kg/t. 100 % of the gold and 32.61 % of the copper in the leaching solution were adsorbed by the resin, and their desorption percentages separately reached 98.59 % and 98.86 % after selective two-stage desorption. The leaching and adsorption percentages of gold first decreased and separately kept at about 91 % and 96 % after 10 solution circulations while the gold desorption percentage and thiosulfate consumption were basically unchanged with solution circulation. The sulfur-oxygen anions in the solution including S2O32–, S3O62–, S4O62–, SO32– and SO42–, and only SO42– was gradually accumulated with solution circulation. SO42–, S2O32– and S3O62– were the main sulfur-oxygen anions adsorbed on the resin, and they did not accumulate obviously on the resin with solution circulation. The novelty of this study is that gold was recovered as elemental gold product based on the the proposed process, and the effect of solution circulation on gold extraction and the accumulation and conversion rules of sulfur-oxygen ions during solution circulation were revealed for the first time.

ECWS: Soil Salinity Measurement Method Based on Electrical Conductivity and Moisture Content

A novel method, ECWS, is proposed for measuring soil initial salinity content (b), based on the soil electrical conductivity EC and soil moisture content WS. This pioneering model rigorously establishes and incorporates the inherent potential correlation among soil bulk conductivity (ECa), soil solution conductivity (ECw), volume water content (θc), and soil salinity content (SSC). First of all, in order to delve the deeper relationship between ECa, ECw, θc and SSC, the soil salinity conductivity conversion coefficient ρa and soil leaching solution salinity conductivity conversion coefficient ρw were employed based on the formula of parallel conducting channels of the soil–water system, and a new measurement model of salinity content was constructed. After that, a mathematical analysis method was used to transform the coefficients of multiple sets of regression equations into matrices to solve ρa, ρw and b. Finally, to validate the accuracy of the proposed ECWS method, verification tests were conducted by utilizing TDR and PWMER sensors. The results with different salinity contents showed that the b size obtained by ECWS model were K2SO4 (1.84 g/kg), NaCl (1.91 g/kg), and KCl (1.92 g/kg). The maximum deviation was less than 0.08 g/kg (relative error less than 5%). The results showed that the influence of different anions and cations on the measurement of salinity content Cl− is greater than that of SO42−, and K+ is greater than that of Na+. This study revealed the relationship between soil electrical conductivity and soil salinity content to a certain extent, and realized the transformation between them, which provided a new method for the measurement of soil salinity content, and also provided a reference for related research on the measurement of soil salinization.

A modified dithionite reduction method for the quantification of iron-bound organic carbon in marine sediments

Iron-bound organic carbon (Fe-OC) plays a significant role in the global marine carbon cycle, facilitating the long-term accumulation and storage of organic carbon. However, the conventional method for quantifying Fe-OC, known as the citrate-bicarbonate-dithionite (CBD) method, has limitations in terms of its efficiency in extracting both Fe-OC and iron (Fe). Another CBD method, commonly used for Fe speciation analysis in paleoenvironmental reconstructions, has shown efficient and selective extraction of Fe oxides; however, its effectiveness in extracting Fe-OC remains uncertain. To evaluate the efficiency of the two CBD methods, synthetic samples spiked with organic acid/environmental organic matter‑iron (hydr)oxide coprecipitates and a marine sediment sample were subjected to extraction. The CBD approach for Fe speciation analysis at pH 4.8 on spiked samples demonstrated higher efficiency compared to the conventional CBD method, but not for samples of marine sediment. This result suggests that the synthetic Fe-OC in the spiked samples did not accurately represent the realistic state of Fe-OC in marine sediments. We found that the pH of the leaching solution during the CBD extraction significantly influenced the efficiency of the Fe-OC and Fe extraction. Our tests at pH 4.8, 5.5, 6.0, 6.5, and 7.0 revealed that lower pH enhanced the extraction of Fe, but hindered the release of Fe-OC. Our study revealed that the new CBD (pH 6.5) method resulted in approximately 30% higher yields of Fe-OC and Fe compared to the conventional CBD method, despite of significant variability in the Fe-OC data. The modified CBD (pH 6.5) method uses lower concentration of extraction reagent and reaction temperature, both of which is considered beneficial. Therefore, we suggest that the new CBD method (pH 6.5) is at least of similar efficiency as the conventional method, and can be employed alongside the established method to facilitate the evaluation of the role of Fe-OC in the marine carbon cycle.

Comprehensive recovery of arsenic and valuable metals from lead smelting flue dust: Process optimization and mechanism investigation

The comprehensive recovery of arsenic and valuable metals from lead smelting flue dust have received widespread attention due to its extremely high toxicity and economic value. In this research, a clean process which consisted of pressure oxidation leaching, preferential separation of Zn and Cd, reduction of As(Ⅴ) and recovery of indium was proposed. Thermodynamic calculation of leaching process suggested that the increasing of temperature reduces the redox potential required for the oxidation of As3+ to As5+, and the optimal conditions were found to be at acid concentration of 100 g/L, oxygen pressure of 2.0 MPa, temperature of 170 °C, L/S of 10 mL/g, leaching time of 2.5 h and agitating speed of 500 r/min. Under the selected conditions, the leaching extents of As, Cd, In, Sb and Zn are 99.17 %, 98.96 %, 92.68 %, 40.23 % and 96.63 %, respectively, while lead remained in the leaching residue. The separation of arsenic and other valuable metals in leachate is the most difficult and critical section of the process, where As2S3 was particularly added to the acid solution in certain manner to preferentially precipitate Zn and Cd in the forms of ZnS and CdS, subsequently reduce As(Ⅴ) to As(Ⅲ). Experiments by adding arsenic filter cake furtherly confirmed the reducibility of As2S3 and realized simultaneous extraction of arsenic in arsenic cake and acid leaching solution. Eventually, arsenic was recovered as As2O3 with a high purity of 98.56 % and the total extraction extent of indium is 93.76 %.

Transformation behavior of hazardous jarosite into recyclable hematite in a solution with high concentrations of K+ and Na+

Iron in the leaching solution with high K+ and Na+ concentrations was usually precipitated as the typical hazardous and toxic jarosite residues. However, this method of treatment has been greatly restricted by increasingly strict environmental regulations. Here we propose that iron can be precipitated from the solution with high K+ and Na+ concentrations as recyclable hematite products by adjusting the concentration ratio of sodium and potassium ions in the solution. The transformation behavior of jarosite into hematite in high concentration potassium ion and sodium ion solution was explained based on collision theory. The results indicated that in instances where the concentration ratio of Na+/K+ is ≥ 4:1, the iron present in the solution can be effectively precipitated as a recyclable hematite product, as opposed to forming the conventional hazardous jarosite residue, even under conditions where the potassium ion concentration reaches levels as high as 4 g/L. On the other hand, thermodynamic and molecular dynamics simulations indicate that at a temperature of 185 °C, the decomposition transformation of Na-jarosite (32.64 kJ and 7.25 eV) is more energetically advantageous compared to that of K-jarosite (61.07 kJ and 15.31 eV). The results were verified by the leaching solution from smelting industry. The iron content in the residues is above 58%, the sulfur content is below 4%, the zinc content is below 1%, and the total iron concentration in the supernatant is about 4 g/L, reaching the production index of the smelting industry. The green, environmentally friendly, and recyclable separation of iron in a solution with high concentrations of potassium and sodium ions is achieved, which is of great significance for the treatment of iron-containing solution and wastewater in the chemical industry and metallurgy fields.

75As Nuclear Magnetic Resonance Spectroscopic Investigation of the Thioarsenate Speciation in Strongly Alkaline Sulfidic Leaching Solutions

Copper ores and concentrates thereof feature an increasingly notable content of impurities such as arsenic and other hazardous elements. As an alternative to the state-of-the-art partial roasting process, arsenic could be removed by the alkaline sulfide leaching of the copper concentrates. In order to optimize and understand the processes, knowledge of the speciation and oxidation states is essential. In addition to methods such as UV/Vis spectroscopy, chromatography and ICP/MS methods, 75As NMR spectroscopy may be useful for the differentiation and quantification of the various species. Although arsenate(V) has been characterized by 75As NMR some time ago, to our knowledge, there are no data on tetrathioarsenate(V) AsS43− and the mixed oxygen/sulfur substituted mono-, di- and trithioarsenates(V) AsOxS4−x3−, x = 3, 2, 1, respectively. Therefore, we investigated several model solutions and samples from Cu-As leaching with 75As NMR. The strongly alkaline conditions of the leaching solution proved to be very advantageous for that purpose. Both the tetrathioarsenate(V) and the mixed species AsOxS4−x3− (x = 1–3) could be characterized and provide valuable data for the quantification of the material flows in the leaching process.

Evolution of physicochemical and leaching characteristics of municipal solid waste incineration fly ash in China under ultra-low emission standard

The physical and chemical characteristics of fly ash has changed significantly under ultra-low emission system and the current leaching system is no longer suitable for high alkalinity fly ash. This work investigated the pH values and evolution of physical and chemical characteristics of fly ash from 24 typical municipal solid waste incineration plants in China. The pH value of the leaching solution obtained by HJ/T 300–2007 presented two different acid and alkali characteristics, where high and low alkalinity fly ash accounted for 54.17% and 45.83%, respectively. The alkali content in fly ash increased significantly after ultra-low emission standard, increasing by 18.24% compared with before the implementation of GB 18485-2014. The leaching behavior of high alkalinity fly ash showed the illusion that they could enter the landfill only by the addition of a small amount of chelating agent or even without stabilization treatment, and its long-term landfill risk is significant. The phase change of high alkalinity fly ash and pH value change of the leaching solution after carbonation were the key factors for the leaching concentration change of heavy metals. Therefore, it is recommended to improve the existing leaching system or conduct accelerated carbonization experiments to scientifically evaluate the long-term leaching characteristics of high alkalinity fly ash, and to reduce the risk of heavy metal release from high alkalinity FA after entering the landfill site.

A new strategy for clean utilization of zinc oxide dust: Preparation of spinel zinc ferrite by solid phase reaction and its catalytic degradation of organic wastewater

The resource utilization of zinc oxide dust (ZOD) is mainly focused on the efficient recovery of zinc by acid leaching at present. Because of a large amount of iron in ZOD and zinc components existing in multi-phase, the problems of low zinc recovery and the separation of zinc and iron ions in the leaching solution are unavoidable. Considering the characteristics of ZOD and the advantages of spinel zinc ferrite (ZnFe2O4) in the advanced oxidation degradation of organic wastewater, a new strategy for clean utilization of ZOD is proposed. The leaching efficiency of soluble zinc components in ZOD reached 96.7 % by selective dissolution with low concentration sulfuric acid solution, and the leaching solution without iron ions can be directly used for electrolytic zinc recovery. The insoluble components of zinc and iron in the leaching residue were converted into ZnFe2O4 by solid phase roasting. By adjusting the roasting temperature, time and molar ratio of Fe/Zn in roasting process, the proportion of zinc elements in the form of ZnFe2O4 reached 99.56 % and a single spinel zinc ferrite product was obtained. Zinc ferrite product activated by ball milling for 2 h (ZFO-2) showed very high catalytic activity in the treatment of organic wastewater by peroxonosulfate (PMS). In the presence of 1 mM PMS and 1 g/L ZFO-2 at 20 °C, the ZFO-2/PMS system achieved a removal rate of over 90 % within 40 min for wastewater containing RhB, MO and MG (10 mg/L). In addition, ZFO-2 is ferromagnetic and easily recovered by magnetic separation. The new strategy proposed in this paper takes into account the efficient recovery of soluble zinc components and the cooperative high-value utilization of insoluble components of zinc and iron in ZOD, which is a comprehensive utilization method with more sustainable resource allocation.

Effective and selective recovery of Au(III) from WPCBs using quaternary phosphonium adsorbent synthesized by adjusting steric hindrance

With the gradual depletion of natural gold ore, waste printed circuit boards (WPCBs) have become one of the most attractive alternatives to gold ore. Here, a series of quaternary phosphonium adsorbents with a large size were successfully synthesized by adjusting the number of functional groups and carbon chain length of functional monomers, which can be used for selective recovery of gold(III) from WPCBs leaching solution. The quaternary phosphonium adsorbent (PS-TEP) prepared by the nucleophilic substitution reaction between triethyl phosphine with the smallest volume and chloromethylated polystyrene (PS-Cl) exhibited the best gold loading capacity (617.90 mg g−1). The adsorption mechanism of gold(III) on PS-TEP surface mainly involves anion exchange between AuCl4− and Cl− in the adsorbent. The charge level of the H atom closest to –CH2–P+ group directly determines the strength of the interaction between the adsorbent and the gold ion. Multiwfn and VMD programs visually confirm the weak interaction between PS-TEP+ and AuCl4−. After 5 adsorption-stripping cycles, the adsorption rate of gold(III) in solution remained at about 99 %. In addition, PS-TEP exhibited good gold(III) selectivity in both simulated and actual WPCBs gold leaching solutions. These results indicate that the large-particle PS-TEP with high capacity is suitable for selective gold recovery from WPCBs leaching solution.

Influence of ionic liquid (R4PSCN) for selective separation and recovery of copper from spent Cu[sbnd]Cr catalyst leach liquor

Separation and recovery of copper (Cu) from sulphate mediated CuCr spent catalyst leach solution through solvent extraction approach has been systematically investigated. A number of Ionic Liquid (IL) and other conventional extractants were used while investigating the selectivity and efficient extraction tendency of either IL or extractants towards Cu(II). In context of copper extraction efficiency, the adopted organic reagents followed the descending order: R4PSCN > R4PD > R4PCy > Cyphos 101 > Aliquot 336 > D2EHPA > Cyanex 272. The extraction behavior of Cu(II) was established based on slope analysis method. From the results it was noticed that extraction occurs through a cation exchange mechanism with association of a mole of Cu(II) per mole of R4PSCN. The plot of log D vs. log [R4PSCN] yield a linear relationship with a slope close to 4 which is used to propose extraction reaction mechanism/ stoichiometry. The nature of complex between Cu(II) and IL was further examined using FTIR analysis of the loaded organic phase with the diluent. Mc-Cabe Thiele diagram was constructed to predict quantitative extraction of Cu(II) which revealed the need for two stages at aqueous to organic (A:O) phase volume ratio of =3:1. The stripping isotherm constructed at optimum NH4OH concentration (0.4 M) suggests the need for two stages at O:A phase volume ratio of = 2:1 for complete stripping of copper with regeneration of R4SCN for further use. Both isotherm conditions were validated by 6 cycles of counter current simulation (CCS) study for obtaining the desired amount of Cu(II) loaded R4SCN (during extraction) and/or stripped copper solution (during stripping). Overall copper enrichment was ∼6 fold leading to produce a copper(II) solution of 48 g/L from 6 g/L Cu(II). The stripped solution was subjected to crystallization study to produce copper sulphate crystals of high purity and was confirmed by XRD analysis of crystal phases.

Impact of desulphurized electrolytic manganese residue-assisted cementitious materials on silicate cement hydration and environmental safety assessment

The use of electrolytic manganese residue (EMR) as a mineral admixture is an efficient way of utilization, but its high content of gypsum phase limits its utilization. In this paper, EMR was desulphurized by means of high temperature reduction roasting to remove the hindrance when utilized as a mineral admixture. The effect of desulphurized EMR (D-EMR) on the formation of major hydration products such as C–S–H and calcium hydroxide (CH), as well as on the degree of hydration of cement clinker, was explored based on mechanical properties, hydration kinetics, thermogravimetry-differential scanning calorimetry (TG-DTG) and Quantitative X-ray diffraction analysis (QXRD). In particular, the mineral phase evolution, the change rule of pore solution and the leaching behavior of heavy metals were simulated in conjunction with thermodynamics. The results show that the D-EMR content of 15 %, comparable mechanical properties and microscopic morphology to the control group can be obtained, while C3S and C2S hydration can be promoted by a factor of 1.08 and 1.28, respectively, without the risk of heavy metal leaching. Based on the thermodynamic simulation of heavy metal solidification by cement clinker minerals, it can be seen that heavy metals in D-EMR composite slurry are solidified mainly by Mn(OH)2 precipitation and weak adsorption effect, and it is safe even at the level of 30 % replacement, provided that the pH value of the leaching solution is greater than 7.5. In addition, the desulphurization technology is feasible from the perspective of environmental protection, and saves 200,000 CNY in emission costs.

Recovery of rare earth elements from rare earth molten salt electrolytic slag via fluorine fixation by MgCl2 roasting

Rare earth fluoride molten-salt electrolytic slag (REFES) is a precious rare earth element (REE) secondary resource, and considerable amounts of REEs exist in REFES as REF3; they are difficult to dissolve in acid or water and impede efficient REE extraction. In REFES recovery, the REF3 species in REFES are usually transformed into acid-soluble rare earth compounds by NaOH roasting or sulfating roasting and then extracted by acid leaching. Moreover, the fluorides in REFES are released as HF gas in the roasting process or enter the liquid phase during the water washing process; both of these processes cause fluorine pollution. Fixing the fluorine into the solid slag provides a way to avoid fluorine pollution. In this study, a novel method was proposed to extract REEs from REFES via MgCl2 roasting followed by HCl leaching. Thermodynamics calculations and thermogravimetry‒differential thermal analyses (TG-DTA) were conducted to investigate the reactions occurring in the roasting process. First, MgCl2 reacts with the REF3 and RE2O3 to form RECl3 and REOCl, respectively. Second, the RECl3 absorbs water and forms RE(OH)3. Third, MgCl2·6H2O is gradually dehydrated to MgCl2·2H2O and reacts with REF3 and RE(OH)3, and REOCl, MgF2 and MgO are formed. Through HCl leaching, the REOCl in the roasting products is leached by HCl acid, while fluoride remains in the solid slag as MgF2. The optimum experimental conditions are as follows: mass ratio of MgCl2 to REFES of 30%, roasting temperature of 700 °C, roasting time of 2 h, hydrochloride acid concentration of 4 mol/L, leaching time of 2 h, leaching temperature of 90 °C and leaching L/S ratio of 20:1. The efficiencies for total leaching of the REEs, La, Ce, Pr, and Nd are 99.13%, 99.20%, 98.42%, 99.38%, and 99.08%, respectively. Moreover, the concentration of fluoride in the leaching solution is 2.191 × 10−6 mol/L. This method has a short process flow with low reagent costs, and the problem of fluoride pollution from REFES recovery is solved; thus, our study has great industrial application potential.

Sulfuric Acid Baking and Fe(III)-Cl--H2SO4 Leaching Behavior of Ni- and Cu-Containing Sulfide and Silicate Rich Suhanko Concentrate.

Ni- and Cu-rich concentrate from a new site in Suhanko, Finland, was investigated. Mineral phases identified included talc, chalcopyrite, kaolinite, and pyrrhotite with 3.2% Cu and 1.5% Ni, and the latter is associated with pyrrhotite. In addition, the concentrate contained the precious elements Pd (14.9 g/t), Ag (17.1 g/t), Pt (2.1 g/t), and Au (1.1 g/t). This concentrate was baked and leached using a Fe(III)-Cl--H2SO4 system. The results showed that the leaching efficiencies of Ni, Cu, and Si from raw concentrate were 60%, 40%, and 5%; however, those from baked concentrate were 96%, 60%, and below 0.1%, indicating that the baking process enhanced Ni and Cu extraction while simultaneously inhibiting the dissolution of Si, which was due to the baking process liberating the associated Ni and Cu by the oxidation of chalcopyrite and pyrrhotite and converting the acid-soluble silicate into an insoluble form. Sulfuric acid leaching solution with Fe(III) as oxidant and Cl- as lixiviant was shown to be effective at leaching Ni (97%), Cu (62%), and Ag (89%), while simultaneously enriching the PMs Pd, Pt, and Au in the residue.

Recovery of gold from electronic waste by the synthesis of Pinus Brutia tannin polymer

Electrical and electronic waste (e-waste) is one of the most common waste problems today and contains many recyclable materials such as gold and palladium. In this study, an adsorption material was prepared by reacting tannin from Pinus Brutia bark with formaldehyde to recover gold from e-waste. The produced Pinus Brutia tannin (PBTR) polymer was characterized using TGA, BET, and FTIR. The adsorption efficiency was investigated using solutions containing gold ions with different pH values, adsorbent masses, initial concentrations, times, and temperatures. The results of these experiments were used to perform adsorption isotherm, kinetics, and thermodynamics calculations. The pseudo-second-order kinetic equation and the Langmuir isothermal equation were found to fit the experimental data best. The Au(III) ion saturation capacity of the PBTR particle monolayer was calculated to be 1771.73 mg/g at 328 K using the Langmuir isotherm. XRD and XPS analyses showed that most of the Au(III) ions were reduced to metallic gold after adsorption on the surface of the PBTR particles. Observations show that the adsorbent effectively removes Au(III) from the leaching solution generated by e-waste.