Dilute Acid Leaching Research Articles

Study on recovering the scattered metals from coal gangue by low-temperature activation and two-stage selective leaching

As metal deposits are developed on a large scale and at high intensity, the strategic metals under “protective measures” will inevitably face resource depletion. It becomes particularly important to sustainably and stably maintain the supply of strategic metals. A method is proposed to selectively extract Li and Ga from coal gangue through a process of ammonium sulfate roasting followed by stepwise leaching. Li and Ga in coal gangue are converted into metal sulfates or ammonium sulfates through low-temperature roasting, and then selectively extracted through a water-acid combined stepwise leaching process. Under the conditions of 450 °C and 2 h, with a coal gangue to ammonium sulfate ratio of 1:2.5, the leaching rates of lithium and gallium reach 88.35 % and 90.28 %, respectively. During the roasting process, ammonium sulfate decomposes into ammonium hydrogen sulfate, which enters the core through the pores of gangue and reacts with kaolinite to enhance activation. Li is converted into lithium sulfate ammonium and extracted through aqueous solution leaching, while metal gallium is first converted into gallium sulfate ammonium and then, with increasing temperature, into ammonium sulfate and extracted through dilute acid leaching.

A low-cost process for complete utilization of bauxite residue

Cost-effective treatment or even valorization of the bauxite residue (red mud) from the alumina industry is in demand to improve their environmental and economic liabilities. This study proposes a strategy that provides a near-complete conversion of bauxite residue to valuable products. The first step involves dilute acid leaching, which allowed the fractionation of raw residues into (1) an aqueous fraction rich in silica and aluminium and (2) a solid residue rich in iron, titanium and rare earth elements. For the proposed process, 91% of the original silicon, 67% of the aluminium, 78% of the scandium and 69% of the cerium were recovered. The initial cost evaluation suggested that this approach is profitable with a gross margin of 167 $US per tonne. This “Residue2Product” approach should be considered for large-scale practices as one of the most economical and sustainable solutions to this environmental and economic liability for the alumina industry.

Effective Leaching of Argillaceous and Dolomitic Carbonate Rocks for Strontium Isotope Stratigraphy

Various methods have been developed to extract a primary seawater Sr isotope signal from carbonate rocks for strontium isotope stratigraphy. However, there is little consensus around the best method due to variable sample purity and mineralogy. For this study, we applied sequential leaching to a range of rock samples in order to explore strontium isotope leaching systematics of less favoured argillaceous and dolomitic limestone samples. Following an ammonium acetate (NH4Ac) prewash that removed ~ 10% of the carbonate fraction, a subsequent dilute acetic acid leach (10–30% aliquot) was shown to extract the lowest, demonstrably least altered seawater 87Sr/86Sr isotope ratios, along with in most cases seawater‐like rare earth element (REE) plus yttrium (Y) patterns with the highest Y/Ho ratios (mostly > 36). Subsequent dissolution steps exhibited significantly elevated 87Sr/86Sr isotope ratios, Rb/Sr, Al/Ca and Mg/Ca ratios, indicating greater contributions from aluminosilicates and dolomite in the leachates. The new dissolution method by comparison significantly increases the likelihood of obtaining primary seawater 87Sr/86Sr isotope ratios from argillaceous and dolomitic limestones where the other established procedures failed. Broad application of this approach could improve the temporal resolution of the seawater Sr isotope curve, especially where high purity limestone samples are scarce.

Selective extraction of rare earth elements from red mud using oxalic and sulfuric acids

Red mud is an alkaline industrial solid waste discharged from alumina production via the Bayer process and can be considered a kind of potential resource of rare earth elements (REEs). Many valuable metals such as iron, aluminum, and titanium also exist in red mud. A multi-stage extraction method was proposed in this study by taking full account of the REEs’ occurrence in red mud. Firstly, the pretreatments of oxalic acid leaching, roasting, and dilute hydrochloric acid leaching were employed to recover iron and enrich REEs in the residue. Subsequently, sulfuric acid leaching was used to selectively dissolve REEs into the leaching solution. Finally, the effects of sulfuric acid concentration, liquid-solid ratio, reaction temperature, and reaction time on the leaching efficiency of REEs were then investigated. The results show that the maximum extraction of the REEs reached 80 % and less than 4 % of Fe, Na, Ca, Ti and Al were extracted under the experimental conditions of 1 mol/L H2SO4, 3 h, 95 °C, and the liquid-solid ratio of 5:1 mL/g. The practicable approach by multi-stage extraction of acid leaching and roasting can split iron and REEs from red mud.

Synchronous extraction of Mn, Pb, Sn, and Se from hazardous electrolytic manganese anode slime (EMAS) via sulfidation transformation and leaching: Rapid separation and sulfidation mechanism

Based on the chemical affinity with sulfur, and solubility and volatility differences of the sulfurized transformed phases, sulfidation treatment of refractory hazardous solid waste can effectively recover valuable metals. In this work, a technically reasonable and efficient treatment of hazardous electrolytic manganese anode slime (EMAS) for rapid and synchronous manganese (Mn), lead (Pb), tin (Sn), and selenium (Se) separation via sulfidation transformation and leaching was proposed. After sulfidation, the valuable elements in EMAS were selectively separated in which the Mn and Sn were converted to soluble salts, whereas Pb was transformed to insoluble sulfate and most Se was volatilized. 70% Se was collected from the volatile dust, 98.1% Mn and 80.5% Sn were transferred to the leachate, while 99% Pb was kept in the leaching residual as the EMAS was treated after sulfidation transformation followed by sulfuric acid leaching under the optimized conditions: roasting with a sulfur/EMAS mass ratio of 1:1 at 400℃ for 10 min, followed by leaching under a sulfuric acid concentration of 8%, a liquid/solid ratio of 10:1, and a stirring rate of 100 r/min at 25℃ for 5 min. Sulfidation kinetics indicated that the sulfidation of manganese oxides was controlled by the interfacial chemical reaction with an activation energy of 35.367 kJ/mol. In terms of efficiency, the low-temperature sulfidation roasting within 10 min and dilute sulfuric acid leaching within 5 min for synchronous separation indicated that the proposed process was reasonable and efficient for hazardous EMAS treatment. For environmental protection, the detrimental SO2 byproduct can be returned to the sulfidation roasting process to reduce the tetravalent manganese or used to make sulfuric acid. The sulfidation and leaching mechanisms for Mn, Pb, Sn, and Se separation were also discussed in detail in this work.

Facile synthesis of zinc ferrite as adsorbent from high‑zinc electric arc furnace dust

A facile route was proposed to prepare zinc ferrite as a heavy-metal adsorption material from high‑zinc electric arc furnace (EAF) dust by roasting it directly with the addition of low-cost Fe2O3, followed by purification via dilute acid leaching. The effect of the addition of Fe2O3, revealed by the Fe/Zn molar ratio, on the formation of zinc ferrite was investigated. The results showed that adding Fe2O3 could increase the percentage of acid-insoluble zinc in the form of zinc ferrite to 94.13% after roasting at 1000 °C for 2 h with the Fe/Zn molar ratio of 1.8. After removing Ca2ZnSi2O7 impurity and nano bead milling, the product could be used as a good adsorbent due to its superior adsorption capacities of 198.26 mg/g, 24.95 mg/g, and 151.45 mg/g for Pb (II), Cr (VI), and Cd (II), respectively. This study offered a novel method for overall and value-added utilization of EAF dust.

Improving Fast Pyrolysis Bio-Oil Yield and Quality by Alkali Removal from Feedstock.

Alkali removal from forest residues, eucalyptus residues, and wheat straw was studied by water and dilute nitric acid leaching. Leaching parameters were optimized for each feedstock in laboratory-scale experiments. After the optimization of leaching on the laboratory scale, nitric acid-leached and untreated feedstocks were pyrolyzed in a bench-scale bubbling fluidized bed unit. In the case of eucalyptus residues and wheat straw, nitric acid leaching was found to increase the organic liquid yield compared to untreated feedstock. In addition, the sugar content of the fast pyrolysis bio-oils was increased, and the alkali content reduced. On the other hand, the pyrolysis experiments with acid-leached forest residues were unsuccessful due to the bed agglomeration. These problems are expected to be a result of the lack of catalytically active elements in biomass which enhance especially the cracking reactions of lignin. Finally, the results were demonstrated in the pilot-scale unit where nitric acid-leached oat straw was pyrolyzed with high organic liquid yield.

Purification of the Acidic Vanadium-Bearing Solution with a Novel Approach of Chemical Precipitation

Calcified roasting followed by dilute sulfuric acid leaching is a promising process for cleaner vanadium extraction from converter vanadium slag. However, some impurities, like Ca, Mg, Mn, Si and Al, also transfer into the leaching solution, accompanying V during the dilute sulfuric acid leaching, leading to the product of vanadium pentoxide prepared from this acidic vanadium-bearing solution, inferior to the product from the traditional process of sodium roasting and water leaching. A chemical precipitation method was firstly proposed to purify this acidic vanadium-bearing solution with a new prepared remover of MnNH4F3, which combines neutralization and fluoride precipitation into one operational step to remove impurities of Ca2+, Mg 2+, Al3+ and Si4+ in an acidic pH range, simultaneously. Effecting factors involved in the purification process were investigated. It was found that removals of Ca, Mg and Al were all over 95% and around 55% of Si was removed as well at stirring speed of 200 rpm, adding coefficient of 1.6, temperature of 50 °C, reaction time of 30 min and pH of 4.50 ± 0.05, while the loss of vanadium was kept lower than 5%, which was attributed to the reason that the purification reactions mainly proceeded on the surface of the remover. Adding flocculant of polyacrylamide was conductive to accelerating sedimentation of the precipitate and reducing the loss of vanadium. Meanwhile, the filter aid of diatomaceous could improve the filtration performance of the slurry. Ammonium persulfate could effectively oxidize and separate Mn2+ in the form of MnO2 from the vanadium-bearing solution which had been treated by MnNH4F3, but performed less selectivity over Mn2+, and the loss of vanadium was unacceptable. The product of vanadium pentoxide prepared from the purified vanadium-containing solution satisfied the requirements for the standard of grade 98.

Recovery of uranium from low-grade tailings by electro-assisted leaching

Approximately 24 billion tons of existing hazardous radioactive waste, such as uranium tailings can yield nearly 9.6 million tons of uranium, which can be made available for nuclear industrial production for almost the next 100 years as per the current consumption levels. However, the extraction of uranium from tailings is highly challenging owing to the high proportion of the gangue content and relatively low content of the soluble U(VI). In this study, we engineered an innovative electro-assisted leaching (EAL) method, based on the dilute acid leaching (AL) method integrated with an electric field, for uranium recovery from low-grade uranium tailings. The proposed method offers advantages in terms of efficiency and environmental pollution control. In our experiments, the EAL method displayed a higher uranium extraction capacity (95%) than the traditional methods (55%) under the same conditions, during a rapid leaching of uranium tailings (containing 0.008% uranium) collected from a radioactive tailings dam in China. The excellent performance of EAL stemmed from (i) the continuous supply of oxidants (ferric ions), which ensured a high uranium solubility (i.e., transformation of U(IV) to U(VI) and (ii) the effect of the electric field on ion migration, which allowed for efficient dissociation of uranium from the complicated multi-mineral composition. In addition, these results demonstrated that EAL could be an efficient and environment-friendly scalable method for extracting valuable metals from low-grade ores or tailings.

Acid Concentration: A Pre-requisite to Enhanced Metal Dissolution?

Technological advancement over the past decade has dramatically changed with new players such as China taking lead in information-technology and telecommunication market across the world. This development has seen surge in manufacturing industry output and consequently raw materials consumed by the sector. The environmental impact is however evident due to human interference with nature. E-waste is the fastest growing waste stream posing serious risk to fauna and flora due to numerous associated pollutants. In recycling industry, hydrometallurgy is widely adopted to recover metals from e-waste. Despite growing concern over secondary pollution associated with disposal, concentrated aqua regia is widely used to extract metals from e-waste. An ultrasonic bath enhanced dilute-acid leaching method was developed to recover copper and lead from waste mobile phone PCB. Repeatability and reproducibility showed 5.3% and 5.0% with respect to Cu while 9.8% and 6.3% RSD were recorded for lead. LOD and LOQ of 0.02 µg/g and 0.064 µg/g (Cu) and 0.082 µg/g and 0.312 µg/g (Pb) revealed that the method is suitable for dissolution of target metals from PCBs. Copper concentration of 332.98 mg/g recorded inferred that dilute aqua regia as much as concentrated has promising metal extraction power and thus could replace concentrated acids.

Groundwater flow system analysis in the regolith of Dodowa on the Accra Plains, Ghana

Study Region: Accra Plains. Study Focus: We conducted a field geology mapping, a well inventory exercise, used ERT, drilled boreholes at 8 locations (15–60 m depth), took drill core samples which we subjected to dilute acid leaching experiments, installed piezometers and equipped them with pressure transducers, analyzed tidal signals in high frequency groundwater hydrographs, carried out pumping tests, and, finally, took 49 groundwater samples. New Insights: Our results indicated a diverse groundwater system. On the one hand, groundwater was found at shallow depths in the saprolite of the Togo Structural Unit (TSU), which, in unweathered state, is composed of phyllites, schists, and quartzites. This system was shallow and predominantly unconfined, as revealed by tidal analysis. In addition, transmissivities of TSU saprolite, all in the order of < 6e-5 m2/s, reduced with depth, which indicated either the lack of a stratiform fractured layer or the presence of such layer beyond drilled depths. On the other hand, groundwater was found in fractures of the gneisses of the Dahomeyan Structural Unit (DSU). This system was potentially deeper, but DSU transmissivities were significantly lower than those of TSU saprolite. Hydrochemically, groundwater was mainly characterized by infiltration of waste-water, evidenced by elevated ion concentrations, including nitrate. Due to the thinly weathered basement, groundwater system development in the area is local and restricted to the Dodowa area.

A novel process for the biological detoxification of non-metal residue from waste copper clad laminate treatment: From lab to pilot scale

A new process of biological detoxification and comprehensive utilization of non-metal residue from waste copper clad laminates treatment was proposed. The process mainly includes microbial cultivation, bioleaching, metal recovery, and wastewater treatment. The leaching rate of metal by bioleaching in acidic environment with pH1.0–2.0 was close to 100% and was 8.7% higher than that by dilute sulfuric acid leaching, and about 11.4% higher than that by circulating tailings leaching. Through a series of continuous batch operation, it was found that Eh (Oxidation/Reduction Potential), pH, c (Cu2+), c (TFe, total iron) of solutions in each section fluctuated within the expected range. Although the concentration of accumulated iron ions in the solution exceeds 20 g/L, the concentration of planktonic microorganisms was still above 6 × 107 cells/mL, and the activated microbial solution still had a good leaching effect on metals in the waste. The residue directly obtained through a filter press had a water content of less than 30%, while that dried residue has a copper content of less than 524 mg/kg. In addition, the grade of sponge copper prepared in the replacement section could reach 86.63%, and the direct yield of copper can reach more than 90%. Furthermore, an economic analysis mainly based on material balance had further confirmed the feasibility of the green treatment process.

Selective recovery of Cr from electroplating nanosludge via crystal modification and dilute acid leaching

Amorphous nanosized particles in electroplating sludge are modified for selective extraction of heavy metals.

Recovery of metals from waste printed circuit boards by selective leaching combined with cyclone electrowinning process

This paper provides a benign process that realized the metals separation and recovery from wPCBs in an efficient and low cost way. The chemical active order and potential-pH diagram of the metals enlightened us to apply stepwise leaching to selective separation of the metals from the wPCBs. The results indicated that the selective separation of Fe, Al, Zn; Sn and Cu can be achieved by the dilute sulfuric acid leaching, displacement leaching using copper sulphate and sulfuric acid leaching with air-oxidization, respectively. Under the optimal conditions, the leaching efficiency of Fe, Al, Zn, Sn and Cu were 92.59%, 90.51%, 89.73%, 1.44% and 0.82%, respectively, in the dilute sulfuric acid leaching. In the displacement leaching, the displacement efficiency of Sn was as high as 95.20%, with little Cu leached. The data of sulfuric acid leaching with air-oxidization experiments shows that the leaching efficiency of Cu reached 95.72%. In order to recover the Sn and Cu in the solutions, the hydrolysis precipitation and cyclone electrowinning were introduced. With these techniques, 92.75% Sn was precipitated and the smooth cathode copper (purity 99.98%) was obtained with the current efficiency was 94.96%. Moreover, the analysis of the mass distribution about the process demonstrated that the H+ and Cu2+ were consumed, but also produced in different procedure, that means the process is a simple and eco-friendly technology, not only due to its high recovery efficiency, but also high reagents recyclable.

Investigating of a Low-Grade Copper Concentrate Desilication by Alkali Pressure Leaching

Low grade copper concentrate, composed mainly of plagioclase, quartz, pyrite, chlorite, chalcopyrite, glauconite, is a promising source for the future recovery of copper and other valuable components, which processing by existing methods are not economical. An alkali pressure leaching method, followed by acid leaching for extraction of aluminum and silica from such low-grade copper concentrate with the aim to enrich other valuable metals content, was explored in this research. The samples were characterized by using wet chemical analysis and X-ray diffraction. An alkali pressure leaching, followed by dilute acid leaching for enrichment of low-grade copper concentrate, allows to extract in a solution of 90,4% Si, 83.82% Al and 7.73% of Cu with the following optimal parameters: NaOH/concentrate-1 mass ratio = 65%, alkali leaching temperature = 240 °C, the alkali leaching time = 90 min. The content of copper in the final concentrate was 19.17%. Consequently, the technology of processing of low-grade copper raw materials is proposed, that allows to increase the comprehensiveness of raw materials usage.

Characterization and thermal decomposition of demineralized wastewater algae biomass

Demineralization pretreatments by leaching using different solvents including deionized water (DI-H2O), acetic acid, formic acid, and sulfuric acid were evaluated for their ash removal efficiency and effects on the physical structure, chemical composition and thermal behavior of wastewater algae biomass (WA). The apparent activation energy of the thermal decomposition (Ea) was estimated using isoconversional methods proposed by Friedman, Flynn-Wall-Ozawa, and Kissinger-Ahakira-Sunose. Dilute-acid leaching substantially reduced the ash content in WA from 40.07% dw (dry weight) to as low as 25.70% dw, with the higher heating value (HHV) considerably improved from 13.08 MJ/kg up to 15.84 MJ/kg. Leaching using formic acid was found the most effective (36.86% ash removal efficiency), while DI-H2O was the least effective (2.94% ash removal efficiency) in reducing the ash content in WA. Both formic acid and sulfuric acid treatments resulted in a decreased of Ea by 10% and 7%, respectively, while no significant change was observed with acetic acid treatment. These results suggest that selective dilute-acid leaching can improve the thermal decomposition of WA, which may benefit subsequent thermochemical conversion processes.

An Environment-Friendly Process Featuring Calcified Roasting and Precipitation Purification to Prepare Vanadium Pentoxide from the Converter Vanadium Slag

Converter vanadium slag is a byproduct of the iron making process when the vanadium titanomagnetite is used as iron raw material. A cleaner process including calcified roasting, dilute acid leaching, precipitation purification, vanadium precipitation with ammonium salt, followed by thermal decomposition was proposed to extract vanadium resource from this slag. And then vanadium pentoxide with purity over 98% was prepared, which can be used as additives for high strength low alloy steel production. A total vanadium recovery beyond 80% was achieved in this whole process. Since no sodium and potassium salt was introduced, wastewater generated was closed-circulating after removing the enriched impurities of P, Si, Ti and Cr with adding powder CaO. The content of V2O5 in residues after vanadium extraction was lower than 1.2 wt.%, while other valuable metals like Fe, Mn, Cr and Ti were concentrated. With no alkaline metal salts added in this process, the metal resources of Fe, Mn, Cr and Ti in the residues were more feasible to be recovered with pyrometallurgy processes.

Effects of mechanical activation on the digestion of ilmenite in dilute H2SO4

Abstract The commercial sulfate process for pigment production uses concentrated sulfuric acid (> 85 wt% H2SO4) as feeding material and discharges 8–10 tons of spend dilute acid (20 wt% H2SO4) per ton of product. Re-using spend acid to leach ilmenite can cut the waste emission and save fresh feeding acid. However, the leaching reaction with dilute acid is very slow and the digestion efficiency is fairly low. This paper describes a wet-milling process to enhance the dilute-acid leaching of ilmenite that makes it possible to produce TiO2 pigment in a more environmentally benign routine. The leaching kinetic study of unmilled ilmenite, dry milled 60 min ilmenite and wet milled 60 min ilmenite was conducted by revision of the shrinking core model (SCM), incorporation of particle size distribution (PSD) into SCM. The results revealed that mechano-chemical activation method significantly increased the leaching efficiency of titanium from 36% to 76% by reducing the particle size and increasing the reaction contact area. On the other hand, the milling process increased the lattice deformation and amorphization of crystalline, which lowered the activation energies in the leaching process. Compared with dry milling operation, wet milling is more effective, the particle size distribution of wet-milled ilmenite was much narrower, smaller, and more uniform. Wet milling of ilmenite makes the leaching reaction with dilute acid (60 wt% H2SO4) practicable and the re-use of spend acid becomes possible and economical.

Zinc recovery from purified electric arc furnace dust leach liquors by chemical precipitation

The present work aims at determining the experimental conditions for the recovery of zinc from leach liquors, produced through dilute sulphuric acid leaching of electric arc furnace dust (EAFD), at atmospheric pressure. Zn can be recovered as an easily filterable precipitate. More specifically, zinc was precipitated by 99.5% with the form of a mixed white fine crystalline powder, comprising of hydrozincite (3ΖnCO3.3Zn(OH)2) and zinc carbonate hydroxide hydrate (ZnCO3.3Zn(OH)2.H2O). Zn precipitation was carried out in a pH range of 6.5–7 at 25°C. The addition of different types of carbonated salts, such as sodium carbonate, sodium bicarbonate or ammonium carbonate, either with the form of suspensions or as solids, was investigated. The produced precipitates were characterized through means of particle size distribution analysis, chemical analysis, X-ray diffraction (XRD), thermogravimetric/differential analyses (TG-DTA) and Fourier transform infrared spectroscopy (FT-IR), whereas their microstructure and morphological characteristics were studied by scanning and transmission electron and microscopy (SEM/TEM). High grade zinc precipitates were obtained, as manganese concentrations did not exceed 1%, whereas traces of Cr, Cu and Pb were also detected.

Process Simulation and Cost Analysis for Removing Inorganics from Wood Chips Using Combined Mechanical and Chemical Preprocessing

Inorganic species (ash) in biomass feedstocks negatively impact thermochemical and biochemical energy conversion processes. In this work, a process simulation model is developed to model the reduction in ash content of loblolly logging residues using a combination of air classification and dilute-acid leaching. Various scenarios are considered, and it is found that costs associated with discarding high-ash material from air classification are substantial. The costs of material loss can be reduced by chemical leaching the high-ash fraction obtained from air classification. The optimal leaching condition is found to be approximately 0.1 wt% sulfuric acid at 24 °C. In example scenarios, total process costs in the range of $6–9/dry tons of product are projected that result in a removal of 14, 62, 39, and 88 % of organics, total ash (inorganics), alkaline earth metals and phosphorus (AAEMS + P), and silicon, respectively. Sensitivity analyses indicate that costs associated with loss of organic material during processing (yield losses), brine disposal, and labor have the greatest potential to impact the total processing cost.