Leaching Duration Research Articles

Effect of fly ash on compressive strength degradation due to calcium leaching procedure

The purpose of this paper is to deal with the influence of fly ash on compressive strength of degraded cement pastes due to calcium leaching. The accelerated experiment has been performed by using a 6 mol/l ammonium chloride solution because natural leaching is a slow process. In order to obtain the mechanical response of different cement pastes, specimens of different water/cement ratios and fly ash contents were prepared. At specified leaching durations, a compression test was performed on the sound and leached specimens. The compression tests show that the loss of compressive strength has a significant linear correlation with the leached ratio of all specimens. This indicates that the decrease in strength is mainly governed by the dissolution of calcium hydroxide. The residual compressive strength loss was related to the mix proportion. The loss of compressive strength increases with water/cement ratios in general. In addition, the addition of fly ash increases the residual compressive strength of totally leached pastes, because more calcium hydroxide is consumed owing to secondary hydration.

Sulfuric acid leaching of South African chromite. Part 1: Study on leaching behavior

The leaching behavior of chromite by sulfuric acid in the presence of oxidant was studied experimentally in this work, where most tests were carried out at 160°C. The results indicated that magnesium and aluminum were leached out together from the silicate phase and porous amorphous silica was produced as a product layer, while the spinel phase gradually shrank with the duration of leaching. The separation of silicate and spinel phases had an influence both on the extraction yield of chromium and the leaching reaction rate by reducing the resistance presented by the silicon-rich phase. It was found that the erosion along the phase boundary was more severe than in other areas, and it can be speculated that groovy corrosion in the spinel phase occurred and developed at the grain boundary. The precipitation behavior of sulfate during the leaching process was also investigated at different temperatures up to 200°C, showing that the sulfate precipitated in the silicon-rich phase at higher temperatures, while the main phase of the sulfate was chromium sulfate, coinciding with results reported by other researchers. All considered metal elements in the spinel phase leached out together in the experiments of this study.

Short time dissolution kinetics of refractory elements Fe, Al, and Ti in Asian outflow-impacted marine aerosols and implications

A six-step sequential extraction protocol was employed for marine aerosols with varying mixture of dust and pollution particles collected from the East China Sea to study the dissolution kinetics of refractory elements Fe, Al, and Ti (with a focus on Fe) in relation to acidic substances such as sulfate, nitrate, and water-soluble organic carbon. The three elements might be of a natural origin such as Asian dust and/or anthropogenic origins such as coal fly ash and biomass burning; however, this study focused on the dissolution kinetics, instead of their sources. We selected three samples with varying dust loading but close acid loadings for the experiment so that the acidic effect on the aerosol Fe dissolution could be explored as the direct contribution of water-soluble Fe from anthropogenic sources, if any, might be constrained at a relatively constant level among the samples. Extraction was stepwise performed with six steps for total 30 min, and the leaching duration was as short as ten seconds in the first five steps. No saturation was found for the analyzed elements. Two phases of dissolution curves were observed in all interested compositions, which could be explained by an aged aerosol particle model, with an intrinsically insoluble core and weathered surface. The first phase curve approximates the first-order reaction, with considerably high dissolution rates of 6.5–277 μmol g−1 min−1, indicating the likely existence of an “extremely fast iron pool” that may exist on the weathered surface of aged particles, along with other three pools proposed by Shi et al. (2011). Acid/dust ratio could be a crucial factor that facilitates parameterization of aerosol iron dissolution. Results of this study are useful in improving aerosol iron and other transition element dissolution schemes in atmospheric chemistry models.

Effect of calcium leaching on the pore structure, strength, and chloride penetration resistance in concrete specimens

In radioactive waste repositories constructed underground and on shorelines, concrete members can remain in contact with groundwater for a long period. However, even pure water creates concentration gradients which lead to the diffusion of Ca ions from the pore water and the degradation of the underground concrete. Therefore, the purposes of this study are to investigate not only the alteration of the pore structure and the loss of compressive strength associated with dissolution but also the characteristics of chloride penetration after leaching-related degradation.The results show that as the leaching period increases, the volume of pores with diameters ranging from 50nm to 500nm is greatly increased. Also, pores larger than 200nm in size rapidly increase in number during the initial leaching time, while those smaller than 200nm increase in number only gradually. Furthermore, the residual strength of the leached part with OPC ranges from 35% to 60%. In addition, those of the mineral admixture replacement ranged from 23% to 50%. The chloride diffusion coefficient measured by the chloride profile increased two-to-five-times with the leaching duration.

Extraction of silver from spent silver oxide–zinc button cells by using Acidithiobacillus ferrooxidans culture supernatant

Abstract The silver extraction from spent silver oxide–zinc button cell battery was investigated by using Acidithiobacillus ferrooxidans ( A. ferrooxidans ) culture supernatant. Parameters such as duration of leaching, volume of culture supernatant, pH, initial shaking speed, and temperature were optimized for the silver extraction. About 98% silver was dissolved in 1 h, at an initial pH of 2.5, 30 °C temperature, 150 rpm shaking speed and by using 50 mL culture supernatant. The use of only culture supernatant for silver extraction indicated that an indirect non-contact leaching was the predominant mechanism for metal solubilization. There was no need for bacteria themselves to be present for the silver extraction. Hence the role of A. ferrooxidans was most likely to regenerate Fe 3+ as an oxidant. The reported method could be considered the first step to recycle spent silver oxide–zinc button cell batteries to overcome pollution problems.

Flexural Strength of Cement Paste Beam under Chemical Degradation: Experiments and Simplified Modeling

This paper presents the findings of a research program that developed prediction equations for estimating the flexural strength of degraded paste beams. Deterioration was attributable to calcium leaching from the beam’s four lateral sides. Given that natural leaching is a slow process, an accelerated experiment was performed by using a 6 M ammonium chloride solution. At specified leaching durations, sound and deteriorated beams were tested in flexure using the three-point bending (TPB) test. The leaching depth and the paste’s compressive strength were both measured. Based on the residual rate of compressive strength and the residual rate of the elastic modulus that was obtained from experimental data, the loss of flexural strength with respect to the leached ratio was constructed with a simplified model. The influence of the residual rate of tensile strength on the prediction and the best-fitting curves are presented. The degradation processes between flexural strength and compressive strength are different.

Leaching Characteristics of Cement-Fly Ash Pastes

The leaching characteristics of cement-fly ash pastes were investigated by MIP, XRD and TG. The results show that the microstructure of hardened cement-fly ash paste deteriorates partly after leaching of soft water. At the leaching duration of 180 days, the hardened paste containing fly ash deteriorated a little more serious than the plain cement paste, but the incorporation of fly ash in a proper ratio was helpful to defer the trend of deterioration of the hardened paste microstructure. The microstructural stability of hardened cement-fly ash paste wasn’t damaged severely during the 180 days leaching duration.

Slow and Fast Transport in Heap Leaching of Precious Metals

Heap leaching of precious metals from low-grade ores is modeled using the slow and fast zone concept of liquid movement in porous media (Kartha and Srivastava Transport in Porous Media 75, 227–247, 2008). The heap is conceptualized as a porous medium with the pores filled by liquid and/or air. The liquid phase is further divided into three zones—immobile, slow moving, and fast moving, with only the immobile and slow-moving liquids interacting with the solid particles. The conceptual model is applied to simulate two- dimensional leaching of a shallow gold ore heap. Temporal evolution of gold concentration in the solid and the liquid phases are analyzed to ascertain the effect of several parameters on the leaching process. Sensitivity analyses are performed with respect to the irrigation rate, the equilibrium sorption coefficient, and the fractional volume of the slow-moving liquid. For a constant volume of the leaching solution and for the same duration of leaching, the metal extraction is higher when a larger number of irrigation cycles are used. The metal extraction is found to be smaller for higher values of the sorption coefficient.

Recovery of ultrafine copper particles from metal components of waste printed circuit boards

Waste printed circuit boards (WPCBs) contain plenty of valuable resources and hazardous materials, considered both an attractive secondary resource and an environmental contaminant. In the current research, a hydrometallurgical process combined ammonia leaching and solvent extraction to recover copper from the metal components of WPCBs, and the production of ultrafine copper particles stripped from a solution was investigated. The results of copper oxidation leaching indicated that 96.7% of copper can be recovered at a temperature of 35°C for a leaching duration of 2h with ammonium sulfate and ammonia concentration of 2mol/L at a solid:liquid ratio of 1:10g/cm3. The treatment of leach liquor for solvent extraction of copper with LIX 84 showed that 50% LIX 84 in kerosene, a 3min period of equilibration, and a pH of 10 were sufficient for the extraction of Cu(II) and 99.6% copper can be recovered from the leached solution. The results of the preparation of copper particles from stripped solution showed that mono-dispersed ultrafine copper particles with a diameter of approximately 1.5μm were obtained from the stripped solution containing 39.25g/L Cu2+ ion, oleic acid used as surfactant, and sodium hypophosphite as reductant. As the purity of the copper extracted from the leaching system was high and the as-synthesized ultrafine copper particles possess excellent anti-oxidation property, this WPCB metal-component hydrometallurgical recycling process has the potential of recovering high-purity ultrafine copper particles.

Hydrocarbon accumulation mechanism and structure of large-scale volcanic weathering crust of the Carboniferous in northern Xinjiang, China

The Upper Carboniferous in northern Xinjiang, China was formed in a post-collisional depression and collapsed structural setting. Within the Upper Carboniferous, volcanic rocks and source rocks alternate over a wide region. At the end of the Carboniferous, these layers were uplifted by plate collisions and subsequently weathered and leached. Volcanic weathering and leaching led to the establishment of weathered crusts that can be divided into five layers. Corrosion and crumble zones in these layers form favorable reservoirs. Volcanic weathering crust formed in sub-aerially exposed paleogeomorphic areas; the five relatively continuous layers are generally preserved in paleogeomorphic lowland and slope regions, but the upper soil layer is usually absent in structurally higher parts of the rock record. The thickness of the weathered layer has a positive nonlinear exponential relationship to the duration of weathering and leaching, and the dynamic equilibrium time of weathered crust is about 36.3 Ma. The thickest weathered layer (∼450 m) is located in fracture zones. Weathered crusts are possible from a range of volcanic rocks with different lithologies, given sufficient time for weathering and leaching. The combination of volcanic weathered crust and source rocks results in three types of hydrocarbon accumulation models: (1) sequences of volcanic weathered crust interbedded with source rocks, (2) a quasi-layered weathered volcanic core located above source rocks, and (3) volcanic rocks associated with pectinate unconformities adjacent to source rocks. Each of these three types has the potential to form a giant stratigraphic reservoir of volcanic weathered crust. This knowledge has changed the traditional exploration model of searching for favorable lithologic and lithofacies zones in volcanic rocks, and has changed the viewpoint that the Carboniferous does not have the genetic potential to be the basement of the basin in northern Xinjiang. The concepts developed here are of great scientific significance and application for focusing oil and gas exploration on volcanic weathered crust. As such, the Paleozoic volcanic weathered crust in the midwestern part of China may possibly contain large-scale stratigraphic reservoirs and thus could be a new oil and gas exploration target in the future.

Experiment study of chemo-mechanical coupling behavior of leached concrete

This paper deal-with concrete behavior under chemical and mechanical degradation. Experimental investigations were described where the effects of the calcium leaching process of concrete on its mechanical properties were highlight. The compressive strength and the stress–strain relationship of leached concrete with different leaching degradations were investigated experimental. As leaching grew, a loss of stiffness and strength were observed and an obvious decrease of peak strain was noted. The leaching degradation was measured by nondestructive or local-damage methods such as phenolphthalein solution, ultrasonic wave and pH value in pores, which showed the better linear relationship of the compressive strength of the leached concrete. The uniaxial compression failure mode of leached concrete was a shear mode under the experimental condition. Then the analytical regression for the stress–strain relationship of leached concrete were given, which could be directly used in theoretical and numerical analysis as well as practical engineering design of leached structures. To quantify the leaching evolution, the leached concrete was analyzed by MIP and TGA. The results showed that the dissolution happened both in portlandite and C–S–H gel during the leaching duration and at the early stages of leaching CH dissolution is the main cause of mass loss. The number of harmful pores with size above 200 nm increased which was associated with the leaching of portlandite, was considered to significantly affect the durability of leached concrete.

Microstructural variation of hardened cement-fly ash pastes leached by soft water

The microstructural variations of hardened cement-fly ash pastes leached by soft water were investigated by MIP, XRD, TG and SEM. The results show that the mass of hardened cement-fly ash paste reduces and its microstructure deteriorates partly after leaching of soft water. At the leaching duration of 180 days, the hardened paste containing fly ash deteriorated a little more serious than the plain cement paste, but the incorporation of fly ash in a proper ratio was helpful to defer the trend of deterioration of the hardened paste microstructure. The microstructural stability of hardened cement-fly ash paste wasn’t damaged severely during the 180 days leaching duration.

Hydrolysis and ion exchange of titania nanoparticles towards large-scale titania and titanate nanobelts for gas sensing applications

One-dimensional titanate and titania nanostructures are prepared by hydrothermal method from titania nanoparticles precursor via hydrolysis and ion exchange processes. The formation mechanism and the reaction process of the nanobelts are elucidated. The effects of the NaOH concentration, HCl leaching duration and the calcination temperature on the morphology and chemical composition of the produced nanobelts are investigated. Na+ ions of the titanate nanobelts can be effectively removed by longer acid leaching and neutralization process and transformed into metastable hydrogen titanate compound. A hybrid hydrogen titanate and anatase titania nanobelts can be obtained under dehydration process of 500 °C. The nanobelts are produced in gram quantities and easily made into nanostructure paper for the bulk study on their electrical and sensing properties. The sensing properties of the nanobelts sheet are tested and exhibited response to H2 gas.

Extraction of indium from zinc plant residues

The main purpose of this study was to extract indium from the Irankoh zinc plant residue. The Irankoh zinc plant residue contained 145 ppm indium. The optimum conditions for leaching of indium and reduction of ferric ion in reductive leaching were obtained at temperature of 90 °C for a leaching duration of 3 h with sulfuric acid concentration of 100 g/L and the amount of required sodium sulfide for reduction of ferric was 1.5 times of stoichiometric quantity of iron. Then, to prepare concentrated indium solution, indium was selectively precipitated from the leach solution. The pH of leach solution was adjusted to 6 with ammonia solution in 90 °C for selective indium precipitation, and reaction time was considered to be 10 min. Then the resulting precipitation was dissolved using hot sulfuric acid solution, and the solution was subject to solvent extraction and cementation using zinc powder to recover indium.

A PROCESS-BASED APPROACH TO ESTIMATING THE COPPER DERIVED FROM RED BEDS IN THE SEDIMENT-HOSTED STRATIFORM COPPER DEPOSIT MODEL

Most estimates of the total tonnage of copper metal leached from footwall red beds to form sediment-hosted stratiform copper deposits are based on the amounts of copper at ppm levels that might have been derived from the volume of red beds underlying given sediment-hosted stratiform copper deposits. That static calculation is replaced here with a process-based approach in which the release of copper results from the progressive diagenetic alteration of the footwall aquifers by oxygen-rich meteoric water driven by topographic recharge in highlands adjacent to the intracontinental rift basins hosting these deposits. The total amount of liberated copper depends on the volume of meteoric water, its oxygen content, and the duration of the diagenetic leaching of copper. Estimates suggest that adequate amounts of copper may be derived from footwall red beds within reasonable periods of early, and possibly more advanced, diagenesis.

The solvent extraction separation of bismuth and molybdenum from a low grade bismuth glance flotation concentrate

The main purpose of this study was to characterize and to extract bismuth and molybdenum from a low grade bismuth glance concentrate. Selective leaching of bismuth could be obtained at a temperature range 60 to 85 °C for a leaching duration of 2 h with hydrochloric acid concentration of 150 gpl, lignin calcium concentration of 0.02 gpl and using a solid–liquid ratio 1/4 g/cc. Treatment of leach liquor for the solvent extraction of bismuth with N235 showed that 8.0 × 10 − 2 M N235 in kerosene, a 3 min period of equilibration and a pH 0.2 were sufficient for the extraction of Bi(III). This bismuth-loaded organic phase was almost completely stripped using 0.5 M EDTA solution. Treatment of leached residue was dealt with by roasting in the presence of slaked lime, and followed by hydrometallurgical treatment of the roasted products. In the lime roasting process, molybdenum recoveries of around 99% were achieved when an excess of 50% lime over stoichiometric requirement was roasted at 700 °C for 2 h and the calcine was leached with 4 M HCl, at 70–80 °C for 2 h. Molybdenum then was effectively extracted from the leached residual solution with N235. An optimum pH of 0.5 was determined for molybdenum extraction. From loaded solvent, this metal was easily stripped with ammonia solutions to give a pregnant solution suitable for final recovery of metal by salt precipitation. Under the optimized conditions, the ultimate recovery rate of bismuth and molybdenum was more than 99% and 98% respectively.

Autoclave processing of the products of catalytic synthesis of industrial diamonds

A process is developed for the autoclave leaching of nickel and manganese with sulfuric acid from the products of catalytic synthesis of industrial diamonds containing 20% Ni and 30% Mn. The optimum conditions for the autoclave processes are determined to be as follows: the temperature range is 150–160°C, the solution acidity is 5 N H2SO4 (230–240 g/l), the leaching duration is 2 h, and the number of processing steps is two. The extraction of the metals into a solution under these conditions is >99% for a total Ni + Co content of <0.4–0.5% in the autoclave leaching cake. The studies performed are related to the search for alternative ways of the catalytic preparation of industrial diamonds that can replace the nonferrous metal leaching technology using aqua regia solutions, which is mainly applied for these purposes under industrial conditions.

Recovery of germanium and other valuable metals from zinc plant residues

The main purpose of this study was to characterize and to extract germanium from the copper cake of Çinkur Zinc Plant. The physical, chemical and mineralogical characterization of the ground copper cake sample obtained from Çinkur showed that it was 84% below 147 μm containing 700 ppm germanium. The copper cake also contained 15.33% Cu, 15.63% Zn, 1.66% Cd, 1.33% Ni, 0.64% Co, 0.35% Fe, 2.62% Pb, 12.6% As, 0.18% Sb and 3.42% SiO 2. The mineralogical analysis indicated the complex nature of the copper cake which was mainly composed of metallic and oxidized phases containing copper, arsenic, zinc, cadmium, etc. The sulfuric acid leaching experiments were performed under the laboratory conditions. The optimum collective extraction of germanium and other valuable metals was obtained at a temperature range 60 to 85 °C for a leaching duration of 1 h with sulfuric acid concentration of 150 gpl and using a solid–liquid ratio 1/8 g/cc. Under these conditions, the recovery of germanium was 92.7% while the other metals were leached almost completely. The optimum selective leaching conditions of germanium was determined as half an hour leach duration, 1/8 g/cc solid–liquid ratio, 100 gpl sulfuric acid concentration and a temperature range 40 to 60 °C. Under these conditions the leach recovery of germanium was 78%. The dissolution's of other metals like cobalt, nickel, iron, copper, cadmium and arsenic were almost low. So, germanium would be separated more selectively at the following precipitation by tannin stage.

Leaching of heavy metals from chromated copper arsenate (CCA) treated wood after disposal

Wood treated by preservatives is commonly found in solid waste. Among the different types of preserved wood, chromated copper arsenate (CCA) treated wood recently has received much attention due to the scale of usage and its significant role in soil and water contamination. As the ash of CCA treated wood would be hazardous if the wood were to be incinerated, this is not a good alternative, and the best available disposal method is thus landfilling in the US, Canada and Australia. Leaching of the metals from preserved wood that is disposed in unlined landfills for construction debris pollutes the soil and water environments. Several factors affecting leaching of the metals from wood, including pH of the leachant, temperature, the duration of leaching and the type of leachant, were investigated. These factors affect each of the metals, chromium, copper and arsenic, differently. A comparison of these effects on each metal was performed. The results of the experiments showed that the pH of the leachants has a significant effect on the leaching process, and sulfuric acid (pH 3) is the most effective leachant compared to nitric and acetic acid (pH 3-4-5). The amounts of leached chromium, copper and arsenic by sulfuric acid (pH 3) during 15 days were, respectively, 0.2, 0.14 and 0.15 mg more than leachates by nitric acid (pH 5) on the basis of 1g of wood (initial contents of 1.03 mg, 0.42 g and 0.8 mg per g of wood). Most of the leaching occurs in the first 5 days, and the rate of leaching decreases significantly after 5 days. Increasing temperature increases the amount of leached metals, and arsenic is the least resistant metal to the leaching when the temperature increases. Increasing the temperature from 15 degrees C to 35 degrees C during 15 days increases the amount of leached chromium, copper and arsenic by acetic acid at pH 5 by about 0.1, 0.4 and 1.2mg per g of wood, respectively.

Simulation of coupled flowing-reaction-deformation with mass transfer in heap leaching processes

Governing equations for a fully coupled flowing-reaction-deformation behavior with mass transfer in heap leaching are developed. The model equations are solved using an explicit finite difference method under the conditions of invariable application rate and constant hydraulic head. The distribution of the degree of the saturation, as well as the distributions of the concentration of the reagent and the solute is given. A cubic relationship between the mineral recovery and the leaching duration is obtained based on the numerical results. The relationship can be used to predict the recovery percentage of the valuable metal.