Leaching Fluid Research Articles

REE geochemistry of gangue minerals and their geological significance in the Muli antimony ore deposit in Yunnan, China

The Muli antimony deposit is located in the Au–Sb polymetallic metallogenic belt in south-eastern Yunnan, China. In this paper, we investigated the concentrations of trace elements in gangue minerals, mainly calcite, quartz, and pyrite, which were formed at different metallogenic stages. Meanwhile, the host rocks, predominantly composed of limestone, are also analysed for comparison. The calcite from the Nadan ore section is enriched with medium-heavy rare earth elements (M-HREEs), likely due to the presence of a high concentration of Fe and Mn impurities, which results in the preferential enrichment of M-HREEs in the calcite. Alternatively, the calcite may be precipitated from the M-HREE-rich granitic leaching fluid. In the Muli ore section, both quartz and pyrite in the metallogenic period show enrichment with light rare earth elements (LREEs), and the wall rock is also enriched with LREEs, which indicates that the wall rock material was involved in the metallogenic process. The W-shaped tetrad effect of quartz in the late metallogenic stage was interpreted to determine extensive fluid–rock interactions in highly fractionated Si-rich systems. Fe and Mn impurities cause M-HREE to be preferentially enriched with calcite to some extent. Whether mineralization is related to granite deserves further study. Eu and Ce anomalies of different types of gangue minerals indicate that the temperature and the fO2 were constantly changing during mineralization, and the temperature of the main ore-stage was higher than 200 °C in an oxidized state. The various REE patterns, LREE/HREE and (La/Yb)N values, reveal that there may be multi-sources and multi-stage hydrothermal activities in the Muli antimony deposit. The REE distribution patterns of minerals are likely interfered with by many internal and external factors. Studies on REE characteristics of calcite, quartz, pyrite and limestone in the Muli antimony deposit have greatly improved the understanding of ore-forming fluids. When we traced the origin and evolution of ore-forming fluids by means of mineral REE distribution patterns, in addition to the determination of inclusions of ore minerals related to mineralization and the in situ analysis methods performed by LA-ICP-MS, we should also combine the REE characteristics of various minerals or trace the ore-forming fluids with multiple methods.

Laboratory studies on leaching of HBCDD from building insulation foams

Abstract A series of laboratory experiments were conducted to study emissions of hexabromocyclododecane (HBCDD) into aqueous leaching fluid under simulated landfill conditions. Expanded (EPS) and extruded (XPS) polystyrene building insulation foam samples containing HBCDD were contacted with deionised Milli-Q water containing 0, 100 and 1000 mg L−1 dissolved humic matter (DHM) as leaching fluid. Concentrations of HBCDD were determined in the resulting fluid and single and serial batch experiments conducted. The impacts on HBCDD concentrations in the leaching fluid temperature and pH were examined. Data from these experiments show that HBCDD concentrations in leaching fluid following contact with EPS and XPS almost all exceeded the aqueous solubilities for each diastereomer and the technical HBCDD formula. This indicates that agitation and abrasion of EPS and XPS were significant mechanisms of HBCDD emission to leaching fluid. Specifically, under such conditions, HBCDD is likely associated with fine abraded particles of the foam and concentrations in the leaching fluid are therefore not limited by the aqueous solubility of HBCDD. Consistent with this, the length of contact time had a significant positive effect on concentrations of all diastereomers in the leaching fluid for XPS and for the least soluble diastereomer, γ-HBCDD for EPS. Generally, the presence of DHM in the leaching fluid and elevated leaching fluid temperatures had significant positive effects on HBCDD concentrations in leaching fluid for both EPS and XPS. Overall, while leaching fluids of pH 8.5 significantly enhanced concentrations of α-HBCDD released from EPS, pH exerts a minor effect on concentrations of HBCDD in leaching fluid.

Application of Geo-electrical Tomography in Coupled Hydro-mechanical–Chemical Investigations in Heap Leaching

A shortcoming of the heap leaching process is its inherent limited metal recovery rate, due primarily to preferential pathways, which reduces the efficiency of the leaching process and can decrease the stability of the heap structure. In this study, geophysical methods were used to characterize the heaps. Five geophysical profiles with 10 m electrode spacing were created on the Miduk heap leaching operations in Iran using mixed array electrode spacing. The dipole–dipole data preserved the high resolution of the surficial response while the dual-direction pole–dipole arrays data provided the desired depth range of 50 m. The inversion of geophysical data revealed areas of focused fluid flow within the heap structure as well as zones of high and low moisture content, and hence areas with a risk of structural failure. In dry zones, under high matrix suction, the hydraulic conductivity is less than in zones with higher water content; thus flow is preferentially focused within the wetter zones, inducing leakage. Geo-electric data also revealed that the three initial heap lifts (oxide lifts) adjacent to the liner were almost impermeable to the leaching fluid due to their fine-grained nature and their high clay content. Oxide materials react more with acid and their structure degrades over time, leaving finer size particles with less permeability. Low permeability zones can cause preferential fluid pathways and pooling to develop elsewhere in the heap, followed by the loss of metal content in those areas. The relationship between these zones is governed by the relative differences in hydraulic conductivity (k) as a function of the water content and matrix suction. If the fluid flux rate is less than the Ksat (saturated hydraulic conductivity) of the fine materials, most of the flow will pass through the fine materials. Therefore, local injection of fluid and changing the fluid flux rate in problematic zones has been suggested. Correlations between resistivity and parameters such as fluid accumulation, copper grade, and slope stability, can be indirectly used to determine the important operational parameters of the heap leaching structures.

Mechanisms of copper stabilization by mineral constituents in sewage sludge biochar

Abstract Sewage sludge has gained increasing attention as one of the most intractable environmental concerns. Pyrolysis is a promising technology that can convert the sewage sludge into biochar and the produced biochar has been increasingly used as adsorbents for heavy metal remediation. However, further environmental problems will be generated from the accumulation of spent biochar after metal adsorption. This work involved a series of experiments to study the adsorption of hazardous copper on the sewage sludge-derived biochar. A novel method was then proposed to stabilize the adsorbed copper in the biochar matrices. The results showed a growth in copper adsorption capacity with an increase in the initial pH of the solutions, and positive effects on copper adsorption were detected from the mineral constituents (e.g., silicon, aluminium, iron and calcium) of the sludge biochar. Furthermore, after copper adsorption, the spent biochar was thermally sintered, and the hazardous copper was found to be incorporated into a CuAl2O4 spinel phase through thermal reactions between copper and the mineral constituents. The stabilization effect on copper was further evaluated in the sintered ceramic products, and copper leachability was found to decrease by a factor of approximately 65 when samples were subjected to a leaching fluid with a pH of 2.9. A series of copper-enriched biochars was prepared to further explain the reaction mechanisms, which showed that aluminium-containing minerals and iron oxide were the most important constituents for copper stabilization. Through this study, a dual effect of the mineral constituents in the biochar was reported on both copper removal and further stabilization, which suggested a strategy to achieve sustainable waste management in an effective and environmentally friendly way.

Microbial communities associated with uranium in-situ recovery mining process are related to acid mine drainage assemblages

A large fraction (47%) of the world's uranium is mined by a technique called “In Situ Recovery” (ISR). This mining technique involves the injection of a leaching fluid (acidic or alkaline) into a uranium-bearing aquifer and the pumping of the resulting solution through cation exchange columns for the recovery of dissolved uranium. The present study reports the in-depth alterations brought to autochthonous microbial communities during acidic ISR activities. Water samples were collected from a uranium roll-front deposit that is part of an ISR mine in operation (Tortkuduk, Kazakhstan). Water samples were obtained at a depth of ca 500 m below ground level from several zones of the Uyuk aquifer following the natural redox zonation inherited from the roll front deposit, including the native mineralized orebody and both upstream and downstream adjacent locations. Samples were collected equally from both the entrance and the exit of the uranium concentration plant. Next-generation sequencing data showed that the redox gradient shaped the community structures, within the anaerobic, reduced, and oligotrophic habitats of the native aquifer zones. Acid injection induced drastic changes in the structures of these communities, with a large decrease in both cell numbers and diversity. Communities present in the acidified (pH values < 2) mining areas exhibited similarities to those present in acid mine drainage, with the dominance of Sulfobacillus sp., Leptospirillum sp. and Acidithiobacillus sp., as well as the archaean Ferroplasma sp. Communities located up- and downstream of the mineralized zone under ISR and affected by acidic fluids were blended with additional facultative anaerobic and acidophilic microorganisms. These mixed biomes may be suitable communities for the natural attenuation of ISR mining-affected subsurface through the reduction of metals and sulfate. Assessing the effect of acidification on the microbial community is critical to evaluating the potential for natural attenuation or active bioremediation strategies.

Leaching of TCIPP from furniture foam is rapid and substantial

A series of laboratory experiments were conducted, in which waste furniture polyurethane foam samples containing tris (1-chloro-2-propyl) phosphate (TCIPP) were contacted with a range of leaching fluids, formulated to simulate the composition of landfill leachate. Leaching was examined under a number of different scenarios, such as: dissolved humic matter concentration, pH, and temperature, as well as the effect of agitation, and waste:leaching fluid contact duration. In addition to single batch (no replenishment of leaching fluid), serial batch (draining of leachate and replenishment with fresh leaching fluid at various time intervals) experiments were conducted. Leaching of TCIPP from PUF appears to be a first order process. Concentrations of TCIPP in leachate generated by the experiments in this study ranged from 13 mg L−1 to 130 mg L−1. In serial batch leaching experiments, >95% of TCIPP was depleted from PUF after 168 h total contact with leaching fluid. Our experiments indicate leaching is potentially a very significant pathway of TCIPP emissions to the environment.

Factors influencing leaching of PBDEs from waste cathode ray tube plastic housings

Samples of waste cathode ray tube (CRT) plastic housings were exposed to Milli-Q® water containing dissolved humic matter at concentrations of 0, 100 and 1000mgL−1 as leaching fluid under laboratory conditions, and polybrominated diphenyl ethers (PBDEs) determined in the resulting leachate. Despite the relatively hydrophobic physicochemical properties of PBDEs, concentrations of ƩPBDEs in the leachate from the leaching experiments in this study ranged from 14,000 to 200,000ngL−1. PBDE leaching appears to be a second order process, whereby a period of initially intense dissolution of more labile PBDEs is followed by a slower stage corresponding to external diffusion of the soluble residue in the material. The bulk of transfer of PBDEs to the leaching fluid occurs within the first 6h of contact, during which time we suggest that the most labile PBDEs are “washed” off the surface of the CRT plastics. The predominant congeners in the chips were BDE-209 (2600mgkg−1) and BDE 183 (220mgkg−1). The impacts on PBDE leaching of leachate pH and temperature were also examined. Increasing the temperature of leaching fluids from 20 to 80°C, enhances the leachability of BDE-209 and BDE-99 from plastics. In all cases, the alkaline pH8.5 examined, resulted in the greatest PBDE concentrations in leachate. Agitation of the waste/leachate mixture enhances PBDE leaching from CRT plastics. Potential evidence for debromination of heavy congeners to the lower brominated and more bioavailable BDEs was observed. Specifically, BDEs-47, -85 and -100 were detected in the leachates, but were absent from the CRT plastics themselves.

Leaching behaviour of hexabromocyclododecane from treated curtains.

A series of laboratory experiments were conducted, whereby two HBCDD treated polyester curtain samples were contacted with deionised Milli-Q water as leaching fluid and HBCDD determined in the resulting leachate. As well as single batch (no replenishment of leaching fluid), serial batch (draining of leachate and replenishment with fresh leaching fluid at various time intervals) experiments were conducted. In single batch experiments at 20 °C, ΣHBCDD concentrations increased only slightly with increasing contact time (6 h, 24 h, and 48 h). This is supported by serial batch tests at 20 °C in which leaching fluid was replaced after 6 h, 24 h, 48 h, 72 h, 96 h, and 168 h. Data from these experiments show that while concentrations of HBCDD in leachate after 24 h cumulative contact time exceed those at 6 h; concentrations in samples collected at subsequent contact times remained steady at ∼50% of those in the 24 h sample. Consistent with this, leaching is shown to be second order, whereby a period of initially intense dissolution of more labile HBCDD is followed by a slower stage corresponding to external diffusion of the soluble residue within the textile. In experiments conducted at 20 °C, α-HBCDD is preferentially leached compared to β- and γ-HBCDD. However, at higher temperatures, the relatively more hydrophobic diastereomers are proportionally more readily leached, i.e. raising the temperature from 20 °C to 80 °C increased concentrations of γ-HBCDD in the leachate by a factor of 28-33 while corresponding α-HBCDD concentrations only increased by a factor of 4.3-4.8.

Evaluating the applicability of regulatory leaching tests for assessing the hazards of Pb-contaminated soils

Soil contamination is a major environmental problem due to the ecological threat it poses. In this work, electron probe microanalysis (EPMA), X-ray diffraction (XRD), and leaching studies were employed to explain the different leaching behaviors of non-stabilized and stabilized soils. The applicability of the leaching fluids used in the toxicity characteristic leaching procedure (TCLP) and Australian Standards, AS 4439.1-1997 for assessing the hazards of contaminated soils was investigated as was the leaching of lead from soil stabilized by cement and buffered phosphate techniques. The results showed Pb speciation in the soil highly influenced metal leaching. The synthetic leaching fluids were unable to provide a reliable estimation of Pb concentration in the municipal landfill leachate (ML) due to the absence of organic ligands capable of forming stable complexes with the lead. Water provided the closest representation of lead leaching from the non-stabilized and phosphate stabilized soils while sodium tetraborate buffer was found to be suitable for cement-stabilized soil in a non-putrescible landfill leachate system. A comparison of stabilization methods revealed that the buffered phosphate technique was more suitable for stabilizing the lead in the soil relative to cement stabilization.

FLUORIDES EVALUATION IN SPENT POT LINER: TOXICITY CHARACTERISTIC LEACHING PROCEDURE LIMITATIONS

The spent pot liner (SPL) is a solid waste generated in the process of aluminum production and is considered hazardous because of its fluoride and cyanide content. The purpose of this study was to analyze the SPL fraction with low cyanide coming from Aluminio Brasileiro S.A. (ALBRAS). For all the pots studied the pH of the spent pot liner (SPL) was very high and ranged from 10 to 11.80. The total fluoride content determined at high pH varied from 5.13 to 11.41 %, while the total fluoride determined in leached fluid at pH 5.0 had low values that ranged from 0.26 to 3.46 %, indicating the low solubility of waste fluorides at low pH values. With leaching fluid above pH 12, the total fluoride content varied from 6.45 to 9.39 %. The experimental results indicate that the Brazilian Standard NBR 10.004, based on leaching at pH 5.0 is not adequate for the classification of hazardous waste, since it underestimates fluoride content.

The design of a full-scale industrial mineral leaching process

The movement of water through the ground is of great industrial importance, and has applications in mining. This paper uses a mathematical model for groundwater flow to present a new design methodology for in situ leaching of minerals. This is a process in which a lixiviant (a solution capable of dissolving the mineral of interest) is pumped into a mineral-bearing rock in order to dissolve the mineral at its own location within the rock itself. The fluid is then pumped to the surface and the mineral is recovered chemically. A major problem with this technology comes from the need to predict accurately where the leaching fluid will go within the ore. Of particular concern is the need to recover as much of the fluid as possible at an appropriate later time. This paper proposes a design strategy that enables the complete recovery of all the mineral leaching fluid, in a full-scale three-dimensional operation. It relies on a spatially periodic arrangement of injection and recovery wells, with a type of secondary recovery process using injected water. The mathematical problem for homogeneous rock is posed, and an extremely accurate asymptotic solution is given. This is sufficient for experimental design purposes. In addition, the full problem is solved numerically using a boundary-integral approach, to investigate limiting cases.

In-Vitro Determination of Arsenic Bioavailability in Contaminated Soil and Mineral Beneficiation Waste from Ron Phibun, Southern Thailand: A Basis for Improved Human Risk Assessment

The post-ingestion bioavailability of arsenic (As) in alluvial soil and mineral beneficiation waste from Ron Phibun, Nakhon Si Thammarat Province, Thailand has been investigated using a physiologically-based extraction test (PBET). The method utilises synthetic leaching fluids closely analogous to those of the human stomach and small intestine, upon which the leaching duration and ambient temperature of the experimental procedure are also directly based. Replicate analyses of Ron Phibun alluvium samples holding 1406 and 2123 μg As g-1 respectively indicated an average stomach absorption of 11.2% (of total soil As). Gross absorption increased to 18.9% following translocation through a simulated small-intenstine regime. Higher gross absorption (35.7%) was recorded during PBET analysis of a flotation waste sample holding c. 2% total As. Within- and between-site variations of As bioavailability can principally be ascribed to mineralogical factors, notably the relative abundances of sulphide, arsenide, arsenate and oxide hosts within the soil/flotation waste matrix. The PBET provides a potentially valuable mechanism for refining risk assessments of sites subject to natural or anthropogenic As contamination. Through the substitution of total soil As values with input data which relate specifically to bioavailable As, risk calculations derived using established models such as the US-EPA package Risk Assistant may prove more realistic, thus facilitating improved cost-benefit analysis of site remediation options. Assessment of the relative human risks associated with potable water consumption and contaminated soil ingestion at Ron Phibun has signified that the latter could constitute a more significant As exposure pathway than recognised previously. Further evaluation of the precise soil ingestion levels of inhabitants residing on the As-rich alluvium which covers much of the district is, therefore, warranted.

Progress toward a mining strategy based on mineral leaching with secondary recovery

The leaching of a mineral from the ground is considered using injection and recovery holes drilled into the rock. In this simplified analysis, the holes are arranged vertically, and an appropriate caustic leaching fluid is introduced into the uppermost hole. The leaching liquor percolates down through the rock, dissolving the mineral of interest, and is pumped out when it arrives at the second hole. Water is introduced at the bottom hole in an attempt to increase the feasible recovery fraction of mineral-bearing liquor. The model problem is solved numerically using a boundary-integral formulation. Maximum feasible recovery fractions for the leaching fluid are obtained and their dependence upon the separation distance between the injection and recovery points and upon the pumping rate for water at the bottom hole are studied. The volume of rock inundated by the leaching liquor is assessed, and a possible practical strategy for in situ leaching of low-grade ores is proposed.

Geochemical stratigraphy and porosity controls in Cretaceous carbonates near the Oman Mountains

Abstract Geochemical stratigraphy is an investigative tool useful (a) for discerning the mode and spatial extent of diagenetic processes in carbonates, (b) for making diagenetic correlations between localities, and (c) for inferring palaeotopography. δ 13 C and δ 18 O stratigraphies of a five-well transect across central Oman indicate that most of the Cretaceous U. Kahmah-Natih interval stabilized under semiclosed, shallow burial, marine-water-like conditions. A ‘depositional’ δ 13 C isotopic signal is preserved. Local anoxic-suboxic events are also recognized, as well as depth-limited effects of early meteoric diagenesis. Isotopic stratigraphic relationships clearly indicate the presence of a local palaeotopographic high in central Oman during deposition of the Natih E member. Good diagenetic-stratigraphic correlations are shown between locations in central Oman and Sharjah, a distance of about 300 miles. Porosity type and distribution within Cretaceous carbonates is related both to early diagenesis and to later structural events. Early cementation associated with marine hardgrounds and subaerial exposure surfaces occluded primary porosity in a limited depth-thickness sense. Later, all existing porosity types were regionally destroyed below the Hawasina thrust sheet in central Oman by thrusting-induced burial stylolitization and associated cementation. Foreland basin carbonates not involved in nappe emplacement retained excellent reservoir properties. Porosity in foreland basin wells consists of primary macro- and micro-porosity, and secondary selective-leach microporosity; selective leaching fluids moved along the subsurface ‘plumbing system’ of the primary porosity-permeability network. Small volumes of pore space were formed in low porosity subthrust carbonates by late aggressive (meteoric?) leaching along fractures and stylolites. Rock texture (facies) did not play a major role in defining the distribution of porosity in the immediate study area.

Leaching of rock fractures: Laboratory and field tests for borehole heat stores

Abstract The aim of this research project was to increase the hydraulic conductivity of fractured rock by pumping a leaching fluid (NaOH) through rock fractures. A 16-week field test was carried out in a borehole heat store consisting of 19 vertical boreholes to a depth of 15 m in gneissic rock. The leaching process was studied simultaneously in a laboratory test where rock samples from core drillings of the test site were used. The hypothesis that NaOH-solution would leach and thereby widen the fractuers, was not fulfilled. On the contrary, the fractures were sealed as the leaching test went on. The explanation for this is that the leaching rate was higher than expected, the leaching fluid was saturated and the dissolved minerals precipitated. In principle, the minerals were dissolved and moved from one part of the fractures to precipitate at another part, causing clogging. The effect of the leaching field test has been simulated by means of a numerical model. The conclusion is that a leaching of rock as described in this paper should be combined with a deposition tank for the clogging material in order to avoid precipitation in the rock fractures. The results of this project have demonstrated a way of sealing rock fractures that has many more applications in engineering geology.

EVOLUÇÃO DIAGÉNETICA DOS TURBIDITOS DA FORMAÇÃO BOM GOSTO NA ÁREA LESTE DA BACIA DE BARREIRINHAS, MA

The Albian BoM Gosto Formation wits deposited in a marine environment during the initial phase of the Barreirinhas Basin formation, in the equatorial Brazilian margin. Arkoses are the main type of sandstones, varying from fine to coarse grained and showing a moderate sorting. These sediments have been subjected to a complex sequence of diagenetic events controlled by basin tectonics and provenance. The main phenomena are the results of chemical reactions in the mesodiagenetic stage. The chronologic sequence of diagenetic processes consists of: 1. mechanical compaction; 2. quartz and feldspar overgrowth; 3. non- ferroan calcite and Fe-calcite cementation and replacement followed by partial dolomitization ; 4. development of secondary porosity essentially by the dissolution of calcite replacement and cement; and 5. porosity reduction by mechanical compaction and precipitation of clay minerals (mainly kaolinite), quartz, feldspar, pyrite and anatase into the pore system, The secondary porosity was classified in four main categories: A, obvious dissolution porosity, subdivided into six classes based on corrosive and/or geometric grain features; B, regular intergranular porosity; C, microporosity, divided into two classes based on the textural position of kaolinite within the framework; and D. fracture porosity. Correlation between porosity classes and depth shows the importance of the ascendant leaching fluids which are responsible for most part of the secondary porosity generation, as well as for the transport of aluminium and silicium, which precipitated as kaolinite under favourable conditions. Silica probably was derived by pressure solution of quartz grains and feldspar replacement by calcite and kaolinite. Carbonate cement probably has its origin related to diagenetic phenomena within the adjacent shales (Arpoador and Tutoia formations). Authigenic clay minerals apparently have been formed through reactions which involved the dehydration of shales. They are the main agents of the low permo-porosity observed in Born Gosto sandstones, once they reduce the secondary porosity and modify the pore system through particle migration and create large amounts of microporosity.

Electrochemical Stability of Embedded Steel and Toxic Elements in Fly Ash/Cement Beds

ABSTRACTThe electrochemical stability in fly ash/cement beds is of major concern to the durability of construction metals (iron or steel) embedded in the matrix as well as the stabilization (fixation) of toxic elements. The electrochemical stabilities were evaluated by measuring the redox potential as a function of both time and leach solution. For simulating the field conditions, the measurements were made on leachates of a prepared solution simulating rain composition in the area of application and results were contrasted to those obtained on leachates of standard deionized water. Two leaching techniques were used: the standard EPA-EP test; a test developed at MRL/PSU for simulating field conditions in which leaching fluids are pumped up a fly ash/cement column. The redox potentials (based on hydrogen scale), Eh's, were plotted vs. pH of the leachates and the regions of stability of various construction materials and toxic elements were predicted. Tafel plots were also constructed for iron in contact with different leachates, and its corrosion rate was estimated.

Solute Travel‐time Estimates for Tile‐drained Fields: III. Removal of a Geothermal Brine Spill from Soil by Leaching

AbstractThe time required to leach a slug of saline, sodic geothermal brine from the point of injection to the tile outlet of an artificially drained field is calculated. Sprinkler, complete, and partial ponding leaching methods are compared as a function of drain spacing and initial location of the spill. Calculated results are presented as dimensionless parameters which scale the drainage system dimensions and the soil water transport properties. Ponded leaching required more water, but less time to leach brine out of the system for all situations except where the brine spill occurs near the midpoint between tile lines.A simple calculation is proposed to estimate the leaching fluid volume required to remove excess Na+ from the exchange complex. Good agreement was attained between simulated and experimental results involving a laboratory soil column. For fine‐textured soils in the Imperial Valley of California it may require up to 30 pore volumes of leaching fluid to replace Na+ with Ca2+ if saturated gypsum solution is used in reclamation. Application time per pore volume was calculated to be in excess of 1 year for all cases except ponded leaching directly over a tile line.