Column Leaching Tests Research Articles

Effect of nickel laterite agglomerate properties on their leaching performance

Heap leaching is a widely used extraction method for low-grade minerals including nickel and cobalt. Agglomeration of fine mineral particles as a precursor to heap leaching is an important means of enhancing leaching rates and metal recoveries. Single pellet leaching behaviour of three nickel laterite ores, namely siliceous goethitic (SG), goethitic (G) and saprolitic (SAP) was investigated to assess the effect of pellet properties (binder type, binder content, porosity and dryness) on its stability, initial leaching rate and maximum Ni recovery. The column leaching performance of agglomerates of the same ores was also investigated. Both single pellet and column leaching tests showed that the ore mineralogy played a major role in the Ni extraction rate, with G-type of ore the lowest. The Ni extraction rate was also found to be directly related to the pellet/agglomerate dryness and the highest rate was obtained at an intermediate degree of dryness due to the better wetting and diffusion of acidic lixiviant into the pores in between the particles. However, no significant effect of drying on the stability of the agglomerates (measured by agglomerate slump in the column) was found in column leaching. For G type of ore, mixing it with high clay ores during agglomeration is recommended to enhance its robustness during leaching process.

Pb and Zn release from intertidal marine sediment in contact with acidified CO2 seawater: Mathematical model for column leaching tests

Variations in the environmental conditions in marine and estuarine environments can lead to the release of metal fractions from the sediment to the seawater phase. The risk of release of potential pollutants from soils and sediment to the aqueous phase is well-assessed through leaching tests. In this work, a mathematical description of the kinetics of Pb and Zn release from marine sediment of the Suances estuary (northern Spain) with CO2 acidified seawater at pH values of 5, 6, 7 and 8 using leaching tests is proposed. The model considers the external mass transfer from the bulk liquid phase to the particle surface and the effective diffusion within the particle itself. Using Aspen Custom Modeler software, the effective solid diffusion values for Zn and Pb are obtained: Def,Zn=1.21×10−12m2/s and Def,Pb=1.56×10−13m2/s. Finally, the solid surface diffusion values for each pH studied value are also calculated. The obtained results would be useful as a line of evidence input for the risk assessment of potential carbon capture and a sequestration site where an advective flow of acidified fluid seawater at different concentrations of CO2 is in contact with recent contaminated sediment.

Long Term Performance of Hydrogeochemical Riverine Mine Tailings Deposition at Freeport Indonesia

Steep terrain, intense rainfall, and seismic activity precluded use of conventional tailings storage facilities at the PT Freeport Indonesia (PTFI) copper-gold mine, in Papua, Indonesia. A controlled river tailings system was adopted as the only feasible way to manage the tailings. The tailings are transported to an engineered 230 km2 deposition area, which is bounded by levees on the east and west sides and is open on the south side to allow transport water and surges of rainfall to exit the area. We evaluated the performance of the ore-fed blending strategy for managing potential acid rock drainage formation of the tailings. Long-term leaching column tests and monitoring of deposited tailings provided insight on the reactivity, leaching behaviours, and neutralizing potential of the samples, and the ratio of acid neutralizing capacity (ANC): maximum potential acidity (MPA) that would ensure that the deposited tailings remain non-acid forming. We concluded that an ANC/MPA ratio >1. 5 provides an adequate factor of safety to prevent acid generation and ensure long-term geochemical stability of the deposited tailings.

Immobilization of Lead from Pb‐Contaminated Soil Amended with Peat Moss

Immobilization of lead (Pb) using soil amendments can reduce Pb toxicity and bioavailability in soil. This study evaluated Pb immobilization in a Pb‐contaminated soil by using peat moss through various tests. The Pb‐contaminated soil (2000 mg Pb·kg−1) was amended with 1%, 5%, and 10% of peat moss to immobilize Pb in the soil. The immobilization properties of Pb in the contaminated soil were evaluated by a column leaching experiment, a microcosm test, and a batch incubation test. Peat moss significantly reduced the Pb leaching in all of the experiments and more effectively reduced mobility and toxicity of Pb in the column leaching and microcosm tests than bioavailability in the batch incubation test. The immobilized lead from the soils amended with 1%, 5%, and 10% of peat moss was 37.9%, 87.1%, and 95.4% from the column leaching test, 18.5%, 90.9%, and 96.4% from the microcosm test, and 2.0%, 36.9%, and 57.9% from the NH4NO3 extraction method, respectively, indicating that peat moss can be effectively used for the remediation of Pb‐contaminated soil.

Leaching of Alkaline Substances and Heavy Metals from Recycled Concrete Aggregate Used as Unbound Base Course

There is an increasing trend toward using recycled concrete aggregate (RCA) in construction. However, concerns have been expressed in laboratory studies about the highly alkaline leachate, high-pH leaching patterns, and release of heavy metals from RCA (e.g., chromium, lead, and arsenic). In this study, RCA materials from a wide geographical area were investigated. Physical, chemical, and mineralogical properties were characterized and laboratory column leaching tests were conducted. Two field test sites were installed and instrumented, one at the Minnesota Road Research (MnROAD) facility in Minnesota and a second at a surface parking facility at the University of Wisconsin–Madison. The MnROAD site showed a neutral leachate pH (between 6.5 and 8.0) after 7 months of service life [1.2 pore volumes of flow (PVFs)]; however, the pH from column leaching tests ranged between 11.0 and 12.5 and showed no decline over 100 PVFs. Because of the large difference between the field and laboratory results, two samples of RCA in Wisconsin, one from a recent demolition of concrete pavement (WR-F) and the other from an RCA stockpile with an age of 5 to 10 years (WR-SP), were used in the Wisconsin field site to verify the Minnesota data and investigate the long-term leaching of alkaline compounds and heavy metals. WR-F RCA started with a high leachate pH (12.6) and remained constant for the first 5 PVFs; however, WR-SP RCA started at a lower pH (7.3) but showed a gradually increasing trend, up to pH = 11.9 for the first 2 PVFs. The pHs from both RCAs were higher than the U.S. Environmental Protection Agency drinking water standard. Arsenic, chromium, lead, and selenium in the RCA field leachate were observed to be higher than the maximum contaminant level for the U.S. drinking water standard.

Treatment of Mine Wastes with Transformed Red Muds (TRM) and Other Iron Compounds: Leaching Column Tests

Leaching column experiments were conducted on sulfide-bearing mine waste material to evaluate the efficacy of transformed red mud (TRM) derived from bauxite refining residue, zero-valent iron, and synthetic iron (III) hydroxides in reducing contaminant mobility. Wastes were placed in columns together with sorbents/reagents in three different setups: as a blended amendment (mixing method), as a bed at the bottom of the column (filtration method), or as a combination of the two previous methods. Results showed that filtration methods are the most effective, whilst the use of sorbents/reagents as amendments leads to unsatisfactory results, because of selective removal.

Leaching Behavior of Aluminum, Arsenic, and Chromium from Highway Structural Fills Amended with High-Carbon Fly Ash

Coal combustion byproducts such as high-carbon fly ash (HCFA) are commonly used in highway construction as a stabilizing agent or soil amendment. Annually, 131 million tons of fly ash is produced in the United States. Unfortunately, only 40% of this fly ash is recycled, most of which are Class C and Class F types. These types of fly ash are generally used in concrete and cement production. However, HCFA cannot be used in such processes because of its high carbon content. Therefore, large amounts of HCFA are being put into landfills and causing significant economic loss and loss of valuable land space. Reuse of HCFA in geotechnical structures, particularly in road embankment construction, keeps these materials out of landfills. However, it is important to determine the environmental suitability of HCFA as a soil amendment because it poses a great potential for metal leaching. To evaluate environmental suitability, a series of column leach tests were conducted to determine the leaching of metals (aluminum, arsenic, and chromium) from soils amended with fly ash. In addition, numerical computer modeling programs were used to predict the metal concentrations in the soil vadose zone and ground-water. Results from laboratory tests indicated that metal concentrations increased with an increase in fly ash content and did not exceed the maximum concentration limits for drinking water, with few exceptions. Numerical modeling techniques predicted that leached metal concentrations decreased in the soil vadose zone with time and that concentrations of leached metals would be below environmental regulatory limits.

Thermal pre-treatment of refractory limonite ores to enhance the extraction of nickel and cobalt under heap leaching conditions

A low grade Western Australian slow-leaching limonite ore (Ore G) was selected to investigate the effect of thermal pre-treatment (roasting) upon the extraction kinetics of nickel and cobalt. The optimised thermal treatment conditions were established using batch roasting and bottle roll leaching tests to determine the effectiveness of each treatment relative to the leach performance of the untreated Ore G. The optimum treatment conditions were then applied to Ore G on a larger scale to provide a bulk sample for subsequent column leach tests. The faster leaching kinetics of both nickel and cobalt of the roasted ore were believed to be partially due to extra surface area created through water escape from goethite during the dehydroxylation process. Interestingly, however, the roasted ore consumes essentially the same amount of acid compared to untreated ore per unit of nickel extracted. Thus roasting of selected ores prior to heap leaching is a pre-treatment that could be applied to the vast WA resource of refractory goethitic ores which are currently not economic to process. The economics, however, would need to be assessed on a case by case basis with the additional processing costs needing to be at least off-set by the value of the recovered value metals.

Leaching behavior of heavy metals and transformation of their speciation in polluted soil receiving simulated acid rain.

Heavy metals that leach from contaminated soils under acid rain are of increasing concern. In this study, simulated acid rain (SAR) was pumped through columns of artificially contaminated purple soil. Column leaching tests and sequential extraction were conducted for the heavy metals Cu, Pb, Cd, and Zn to determine the extent of their leaching as well as to examine the transformation of their speciation in the artificially contaminated soil columns. Results showed that the maximum leachate concentrations of Cu, Pb, Cd, and Zn were less than those specified in the Chinese Quality Standards for Groundwater (Grade IV), thereby suggesting that the heavy metals that leached from the polluted purple soil receiving acid rain may not pose as risks to water quality. Most of the Pb and Cd leachate concentrations were below their detection limits. By contrast, higher Cu and Zn leachate concentrations were found because they were released by the soil in larger amounts as compared with those of Pb and Cd. The differences in the Cu and Zn leachate concentrations between the controls (SAR at pH 5.6) and the treatments (SAR at pH 3.0 and 4.5) were significant. Similar trends were observed in the total leached amounts of Cu and Zn. The proportions of Cu, Pb, Cd, and Zn in the EXC and OX fractions were generally increased after the leaching experiment at three pH levels, whereas those of the RES, OM, and CAR fractions were slightly decreased. Acid rain favors the leaching of heavy metals from the contaminated purple soil and makes the heavy metal fractions become more labile. Moreover, a pH decrease from 5.6 to 3.0 significantly enhanced such effects.

Evaluation of different amendments to stabilize antimony in mining polluted soils

Soil pollution with antimony is of increasing environmental concern worldwide. Measures for its control and to attenuate the risks posed to the ecosystem are required. In this study the application of several iron and aluminium oxides and oxyhydroxides as soil amendments was evaluated in order to assess their feasibility to stabilize Sb in mining polluted soils. Mine soils with different pollution levels were amended with either goethite, ferrihydrite or amorphous Al oxide at various ratios (0–10%). The effectiveness of such treatments was assessed by both batch and column leaching tests. The use of ferrihydrite or amorphous Al oxide proved to be highly effective to stabilize Sb. Immobilization levels of 100% were found when doses of 5% ferrihydrite or 10% amorphous Al oxide were applied, regardless of the soil Sb load. Column leaching studies also showed a high Sb leaching reduction (>75%) when soils were amended with 1% ferrihydrite or 5% amorphous Al oxide. Moreover, such treatments proved to simultaneously immobilize As and Pb in a great extent when soils were also polluted with such toxic elements.

Evaluation of Leaching Protocols for Testing of High-Carbon Coal Fly Ash–Soil Mixtures

Beneficial reuse of coal combustion byproducts, e.g., in highway construction, requires an evaluation of metal leaching potential. Metal leaching from high-carbon fly ash in soil mixes typical of highway embankment construction was evaluated using different soil-fly ash mixtures and three common leaching tests: the water leach test (WLT), the Toxicity Characteristic Leaching Procedure (TCLP), and the column leach test (CLT). The effect of test methodology and pH on Cu, As, and Cr leaching was examined. TCLP concentrations for Cu and As exceeded those from WLTs in the majority of mixtures due to lower pH conditions, while Cr was higher in the WLT for alkaline fly ash mixtures. Maximum CLT concentrations were higher than TCLP and WLT concentrations for the majority of mixtures, but usually decreased rapidly, suggesting that leachate concentrations might initially exceed regulatory limits, but only for a short time. A comparison of leaching results is discussed as a framework for the development of a flexible, integrated leaching protocol incorporating elements of batch and column leach tests to provide more accurate, site-specific leaching predictions given time and cost constraints. DOI: 10.1061/(ASCE)EE .1943-7870.0000668. © 2013 American Society of Civil Engineers. CE Database subject headings: Fly ash; Chromium; Copper; Arsenic; Coal; Soils; Mixtures; Recycling. Author keywords: Leaching; Fly ash; Batch leach test; Column leach test; Chromium; Arsenic; Copper.

Simultaneous stabilization of arsenic, lead, and copper in contaminated soil using mixed waste resources

In the present study, stabilization treatment using waste resource stabilizers was performed for soil contaminated with As and heavy metals (Pb and Cu). Calcined oyster shell (COS) and coal mine drainage sludge (CMDS) were used as a mixed stabilizing agent for a wet-curing duration of 28 days. After the stabilization treatment, the treatment process efficiency was evaluated by the results of various batch- and column-leaching tests. Neutral and weak acid extraction methods, such as water-soluble extraction and SPLP, did not exhibit satisfactory results for heavy metal stabilization, even if they showed very low leachability. On the other hand, TCLP and 0.1 M HCl extraction showed that the stabilizers significantly reduced the amount of heavy metals leached from the soil, which strongly supports the thesis that the stabilization treatment is efficient in the acidic leaching conditions that were explored. Specifically, in the 0.1 M HCl extraction, the reduction efficiencies of As, Pb, and Cu leachings were more than 90 %, compared with control experiments. This study demonstrates that the application of waste resources for the stabilization of As and heavy metals is feasible. However, some limitations observed in the experiments should be considered in future studies, such as the mobilization of alkali-soluble elements, and in particular, exchangeable fractions of Cu. In addition, the treatment efficiency can be evaluated by different leaching methods, which suggests that multidirectional approaches are required for the proper evaluation of stabilization treatment.

Evaluation through column leaching tests of metal release from contaminated estuarine sediment subject to CO2 leakages from Carbon Capture and Storage sites

The pH change and the release of organic matter and metals from sediment, due to the potential CO2 acidified seawater leakages from a CCS (Carbon Capture and Storage) site are presented. Column leaching test is used to simulate a scenario where a flow of acidified seawater is in contact with recent contaminated sediment. The behavior of pH, dissolved organic carbon (DOC) and metals As, Cd, Cr, Cu, Ni, Pb, Zn, with liquid to solid (L/S) ratio and pH is analyzed. A stepwise strategy using empirical expressions and a geochemical model was conducted to fit experimental release concentrations. Despite the neutralization capacity of the seawater-carbonate rich sediment system, important acidification and releases are expected at local scale at lower pH. The obtained results would be relevant as a line of evidence input of CCS risk assessment, in an International context where strategies to mitigate the climate change would be applied.

Effect of loess for preventing contamination of acid mine drainage from coal waste

Acid mine drainage (AMD) that releases highly acidic, sulfate and metals-rich drainage is a serious environmental problem in coal mining areas in China. In order to study the effect of using loess for preventing AMD and controlling heavy metals contamination from coal waste, the column leaching tests were conducted. The results come from experiment data analyses show that the loess can effectively immobilize cadmium, copper, iron, lead and zinc in AMD from coal waste, increase pH value, and decrease Eh, EC, and SO 4 2− concentrations of AMD from coal waste. The oxidation of sulfide in coal waste is prevented by addition of the loess, which favors the generation and adsorption of the alkalinity, the decrease of the population of Thiobacillus ferrooxidans, the heavy metals immobilization by precipitation of sulfide and carbonate through biological sulfate reduction inside the column, and the halt of the oxidation process of sulfide through iron coating on the surface of sulfide in coal waste. The loess can effectively prevent AMD and heavy metals contamination from coal waste in in-situ treatment systems.

Column leaching test to study effect of cover of fly ash for preventing acid mine drainage from coal waste

Coal waste that releases highly acidic, sulfate and metals rich drainage is a serious environmental problem which causes the contamination of surface and ground water as well as soils in coal mining areas in China. In order to study the effect of using fly ash for preventing acid-mine drainage and controlling heavy metals contamination from coal waste, two column leaching tests were conducted to determine if a cover of fly ash could be used for the control of acid-mine drainage from coal waste. We investigated the effect of the cover of fly ash on controlling acid, sulfate and heavy metals contamination from coal waste. The results from the experimental data analyses show that the cover of fly ash can effectively immobilize cadmium, copper, iron, lead and zinc in acid-mine drainage from coal waste, increase the pH value from 2.0 to 7.5 and decrease Eh from 249 mV to 148 mV, EC from 5.22 mS/cm to 1.05 mS/cm and SO42- concentrations from 12911.7 mg/L to 881.4 mg/L of acid-mine drainage from coal waste. The immobilization rate of heavy metals reached 99%. The oxidation of sulfide minerals in coal waste was prevented by the cover of fly ash, which favors the generation of alkalinity, the decrease of the population of Thiobacillus ferrooxidans, the heavy metals immobilization by precipitation inside the column, and the halt of the oxidation process of sulfide through iron coating on the surface of sulfide minerals in coal waste. The cover of fly ash can effectively control acid-mine drainage and heavy metals contamination from coal waste in situ treatment systems.

Leachability of elements in alkaline and acidic coal fly ash samples during batch and column leaching tests

Three acidic (HA, HB, and MA) and one alkaline (PD) fly ash samples collected from four different power plants were subjected to batch and column leaching tests to evaluate the leachability of several elements. Jar leaching tests (up to 120h), serial batch leaching tests (35days), and long-term (up to 70weeks) batch leaching tests were performed using doubly deionized (DDI) water, and column leaching tests (131–150 pore volumes) were conducted using a synthetic acid rain (SAR) solution. The results of batch and column leaching tests showed that different proportions of As, Cr, Mo, Sb, Se, and V were leached by DDI water and SAR from the four fly ash samples. The increasing leachate concentrations of As, Cr, Mo, Sb, Se (except PD fly ash), and V with time indicated that the long-term release of these elements was controlled by the dissolution of glassy fly ash particles. Mobilization of As from HA fly ash, Cr from PD fly ash, and Se from both HA and PD fly ash also showed a bimodal leaching pattern during column leaching tests, potentially indicating the association of these elements with different fly ash fractions. In general, Mo, Sb, and Se showed high mobilities, while only small amounts of Cr were released from the fly ash samples. Boron, Ca, K, Mg, Mn, and Na were released very rapidly during the initial phases of both serial and column leaching tests. These elements were likely enriched in surface-bound, highly soluble loose particles. During long-term batch leaching tests, HB and MA fly ash leachate concentrations of Ba, Co, Mn, Ni, and Zn decreased with time, indicating possible adsorption or co-precipitation with secondary minerals. Because many of the older fly ash disposal facilities are unlined, these sites are potential sources of hazardous elements to the environment. Therefore, development of effective and economic methods to contain trace elements within the disposal facility site is desirable to prevent contamination of groundwater and surface water resources.

Mobility of Metals from Fly Ashes and its Potential Impact on Surface Water Quality in Guizhou Province, Southwestern China

In order to evaluate the impacts of metals mobility from fly ashes on surface water quality, the dissolved metals concentrations in the stream and pond waters nearby fly ash piles were investigated at the thermal power plant regions in central Guizhou Province, and batch leaching or column leaching tests for the fly ashes were performed. The results shown that the most mobile of the metals leached were Cu, Cr, Pb and Cd from fly ashes and the concentrations of the metals in leachate solutions increased with the amount of fly ashes, and high concentrations of Pb (0.040~0.886 mg L−1), Cr (0.025~0.315 mg L−1) and Cd (0.007~0.052 mg L−1) in the leachates from fly ashes, and then there is an mobility of dissolved metals to the surface waters impacted by the runoff or leaching water. In thermal power plant areas, the concentrations of Pb, Cr and Cd in the stream waters and the pond waters nearby fly ash piles were 0.024~0.374 mg L−1, 0.030~0.212 mg L−1 and 0.014~0.035 mg L−1, respectively, as indicated by high concentrations of Pb, Cr and Cd, making it unsuitable for human drinking, suggesting a environmental problem of runoff or leaching water from fly ash pile in those areas.

Acid–base accounting assessment of mine wastes using the chromium reducible sulfur method

The acid base account (ABA), commonly used in assessment of mine waste materials, relies in part on calculation of potential acidity from total sulfur measurements. However, potential acidity is overestimated where organic sulfur, sulfate sulfur and some sulfide compounds make up a substantial portion of the sulfur content.The chromium reducible sulfur (CRS) method has been widely applied to assess reduced inorganic sulfur forms in sediments and acid sulfate soils, but not in ABA assessment of mine wastes. This paper reports the application of the CRS method to measuring forms of sulfur commonly found in mine waste materials. A number of individual sulfur containing minerals and real waste materials were analyzed using both CRS and total S and the potential acidity estimates were compared with actual acidity measured from net acid generation tests and column leach tests. The results of the CRS analysis made on individual minerals demonstrate good assessment of sulfur from a range of sulfides. No sulfur was measured using the CRS method in a number of sulfate salts, including jarosite and melanterite typically found in weathered waste rocks, or from dibenzothiophene characteristic of organic sulfur compounds common to coal wastes.Comparison of ABA values for a number of coal waste samples demonstrated much better agreement of acidity predicted from CRS analysis than total S analysis with actual acidity. It also resulted in reclassification of most samples tested from PAF to NAF. Similar comparisons on base metal sulfide wastes generally resulted in overestimation of the acid potential by total S and underestimation of the acid potential by CRS in comparison to acidity measured during NAG tests, but did not generally result in reclassification. In all the cases examined, the best estimate of potential acidity included acidity calculated from both CRS and jarositic S.

Experimental and numerical analysis of metal leaching from fly ash-amended highway bases

A study was conducted to evaluate the leaching potential of unpaved road materials (URM) mixed with lime activated high carbon fly ashes and to evaluate groundwater impacts of barium, boron, copper, and zinc leaching. This objective was met by a combination of batch water leach tests, column leach tests, and computer modeling. The laboratory tests were conducted on soil alone, fly ash alone, and URM–fly ash–lime kiln dust mixtures. The results indicated that an increase in fly ash and lime content has significant effects on leaching behavior of heavy metals from URM–fly ash mixture. An increase in fly ash content and a decrease in lime content promoted leaching of Ba, B and Cu whereas Zn leaching was primarily affected by the fly ash content. Numerically predicted field metal concentrations were significantly lower than the peak metal concentrations obtained in laboratory column leach tests, and field concentrations decreased with time and distance due to dispersion in soil vadose zone.

Leaching of Metals from Fly Ash–Amended Permeable Reactive Barriers

AbstractOne potential beneficial reuse of high-carbon-content (HCC) fly ashes is in reactive barrier applications for remediation of contaminated groundwater. However, leaching of metals from coal fly ashes into the environment is of concern. A series of column leach tests (CLTs) and batch water leach tests (WLTs) were performed to investigate the potential leaching of metals from HCC fly ashes during reactive barrier applications. Fly ash content and pH were two key factors affecting the amount leached in WLTs. Leaching of metals in CLTs exhibited a first flush, followed by a tailing elution pattern, for all fly ashes. Attempts to correlate the WLT and CLT data indicated that scale-up of the WLT results to the column experimental setup provided a better prediction of the leachable amount in CLTs compared with a direct comparison of concentrations. Nevertheless, caution should be exercised when building correlations because of the different testing conditions in the two test setups.