Tank Leaching Test Research Articles

Study on the leaching behavior of cemented paste backfill containing arsenic trioxide roaster waste

After decades of mining at Giant Mine in Yellowknife, Northwest Territories, a significant amount of arsenic trioxide roaster waste (ATRW), containing around 60% arsenic, was stored underground, posing serious health hazards. This study explored solidification and stabilization of ATRW through its incorporation into cemented paste backfill (CPB). It evaluated the stability of arsenic-bearing compounds and the mechanisms of arsenic trioxide stabilization within CPB. Based on the results of unconfined compressive strength (UCS) tests on CPB samples, certain samples were selected for monolithic tank leaching tests (TLT) and a range of microstructural analyses, including thermogravimetry, X-ray absorption spectroscopy, Fourier-transform infrared spectroscopy, and computed tomography. These tests aimed to examine the leaching behavior of arsenic and the microstructure of the selected CPB samples, and to investigate the relationship between their strength, leaching behavior, and pore characteristics. Findings indicated significant arsenic release from CPB surfaces. Up to 41% of arsenic was leached from the CPB samples, and the leaching of arsenic, calcium, and sulfate showed no signs of stabilizing, suggesting potential long-term leaching risks. The pH levels ranged between 9.2 and 10.0, with the dissolution of ATRW contributing to a decrease in pH. This lower pH inhibited the formation of portlandite, while calcium-silicate-hydrate (C-S-H) gels were identified as the primary hydration product, albeit in limited quantities. Thermogravimetric analysis showed weight losses primarily due to calcite decomposition, while X-ray absorption spectroscopy revealed arsenic was present predominantly in its + 3 oxidation state, with no significant As-Ca bonding observed in high-strength samples. CT scans highlighted a relationship between higher strength and larger pore volumes. The study concluded that while ATRW incorporation in CPB can provide mechanical stability, modifications are necessary to reduce arsenic solubility and mitigate environmental risks.

Leaching behavior of sustainable concrete made with coal ash wastes as replacement of cement and sand.

The coal-fired power plant fly ash (FA) and bottom ash (BA) are gradually used as alternative materials in the concrete. However, knowledge of the leaching characteristics of using both incinerator ashes in concrete production is lacking. This work aimed to evaluate the leaching behavior of the FA and BA used in concrete production by employing batch and tank leaching tests. The outcomes of both leaching tests showed that there was no considerable leaching of any trace elements to the environment, and it remains much lower than standard limitations for utilization as construction materials. The results of cumulative mass discharge showed that the slope of flux time for all elements was less than 0.4 and because of that, primary surface wash-off was the main discharge process of all the heavy metals. Strength test results revealed that there was not much difference between coal ash concrete (CAC) and the control mix at the initial age of curing time. Despite that, at a long period of curing time (180 days), the compressive strength of CAC containing 20% FA as cement replacement and 100% BA as fine aggregate replacement increased by 76% due to the pozzolanic reaction of BA and FA in comparison to the normal concrete, while, due to the high porosity of BA, the workability of CAC decreased by 50%. The outcomes of the current work revealed that the combined use of FA and BA can be counted as a promising alternative in the production of sustainable concrete for structural applications toward sustainable development.

Effect of in situ CO2 mixing of cement paste on the leachability of hexavalent chromium (Cr(VI))

In situ CO2 mixing technology is a potential technology for permanently sequestering CO2 during concrete manufacturing processes. Although it has been approved as a promising carbon capture and utilisation (CCU) method, its effect on the leachability of heavy metals from cementitious compounds has not yet been studied. This study focuses on the effect of in situ CO2 mixing of cement paste on the leaching of hexavalent chromium (Cr(VI)). The tank leaching test of the CO2 mixing cement specimen resulted in a Cr(VI) cumulative leaching of 0.614 mg/m2 in 28 d, which is ten times lower than that of the control mixing specimens. The results in thermogravimetric analysis indicated that a relatively significant amount of CrO42− is immobilised as CaCrO4 during the CO2-mixing, and a higher Cr–O extension is observed in the Fourier transform infrared spectra. Furthermore, a portion of the monocarboaluminate is inferred from microstructural analyses to incorporate CrO42− ions. These results demonstrate that in situ CO2 mixing is beneficial not only in reducing CO2 emissions, but also in controlling the leaching of toxic substances.

Kinetics and toxicological potential of heavy metal leaching from asphalt pavements

The leaching of heavy metals from asphalt pavement has attracted increasing attention due to its associated environmental risks. Comprehending the leaching process is crucial for ensuring the safe utilization of asphalt pavement. This study investigates heavy metal leaching kinetics from asphalt pavements using tank-leaching tests and dynamic simulations employing both first and second-order kinetic models. Furthermore, this study reveals the toxicological potential of heavy metal leaching from asphalt pavement by assessing its temporal metal accessibility based on the obtained kinetic attributes. Six distinct asphalt mixtures were prepared and tested, each exhibiting two different gradations. The findings demonstrated that both kinetic models effectively elucidated the leaching process. Notably, the relatively stable final leaching stages primarily adhered to first-order kinetics, while the second-order kinetics provided a superior description of the more intricate initial leaching stages. In terms of toxicological potential, the results indicated that recycled waste-incorporated asphalt pavements, specifically bottom ash-incorporated asphalt and asphalt rubber, exhibited excessive heavy metal leaching for varying durations, ranging from several days to months under specific conditions. This study has provided valuable insights into the metal leaching kinetics of asphalt pavements and their associated toxicological impact, significantly advancing the current understanding of the consequences of heavy metal leaching from asphalt pavements.

Leaching behaviour of a crystallisation inhibitor in mortars

This paper investigates the leaching behaviour of sodium ferrocyanide, a known crystallisation inhibitor of sodium chloride, which is added to mortars for mitigation of salt decay. Leaching and depletion of the inhibitor is a practical performance related issue that might over time, make the inhibitor less effective against salt decay. In this research, the inhibitor was added to natural hydraulic lime (NHL) mortars during the mixing stage. Leaching of the inhibitor from the hardened mortar was assessed experimentally in laboratory. Both diffusion- and advection-driven transport mechanisms were considered. Diffusion experiments were carried out in a tank leaching test setup. Capillary absorption and drying cycles were used as a driving force to study advection-driven transport. Quantification of the leached species was carried out using various analytical techniques, including UV-VIS spectroscopy, ICP-OES and ion chromatography. The results from the tank leaching test show a high effective diffusion coefficient of ferrocyanide ions, in the same order of magnitude as sodium chloride transport. The advection test shows accumulation of the inhibitor at the evaporative surface and depletion of the inhibitor in the inner layers with successive wet-dry cycles. Based on these results it can be inferred that the degree of inhibitor leaching is significant and needs to be minimised to prolong the positive effect of the inhibitor on mortar durability. Potential solutions to reduce inhibitor leaching are discussed.

Evaluating the impact of drying on leaching from a solidified/stabilized waste using a monolithic diffusion model

The release rates of constituents of potential concern from solidified/stabilized cementitious waste forms are potentially impacted by drying, which, however, is not well understood. This study aimed to identify the impacts of drying on subsequent leaching from Cast Stone as an example of a solidified cementitious waste form. The release fluxes of constituents from monoliths after aging under 100, 68, 40, and 15 % relative humidity for 16, 32, and 48 weeks, respectively, were derived from mass transfer tank leaching tests following EPA Method 1315. A monolithic diffusion model was calibrated based on the leaching test results to simulate the leaching of major and redox-sensitive constituents from monoliths after drying. The reduction in physical retention of constituents (tortuosity-factor) in the unsaturated zone was identified as the primary impact from drying on subsequent leaching. Fluxes of both major (i.e., OH–, Na, K, Ca, Si, and Al) and redox-sensitive constituents (i.e., Tc, Cr, Fe, and S) from monoliths during leaching were well described by the model. The drying-induced reduction of tortuosity-factor and concomitant changes in porewater pH and redox conditions can significantly change the subsequent release fluxes of pH- and redox- sensitive constituents.

Heavy metal and metalloid emissions during co-processing of waste in a sintering kiln: Migration characteristics in the kiln and long-term leaching from bricks

Heavy metals (HMs) in mixed hazardous waste can be volatilized in the kiln for preparing sintered bricks, which greatly increases the environmental risk. In this study, the volatilization, transformation, and leaching of HMs from bricks were evaluated. Field tests and laboratory leaching experiments were carried out. HM-contaminated soil was used to prepare sintered bricks at high-temperature in a tunnel kiln. Release of HMs from brick under rainfall conditions was investigated in laboratory simulation experiments. The field tests showed that the total amount of Pb, Zn, Cd distributed to the gas phase were all less than 2%, but the amount of Hg entering the gas phase 40.1%–60.5% in the particulate forms. The As leaching rate increased after sintering of bricks in the kiln, which was attributed to the increased formation of soluble arsenate and the reduced availability of sorption sites. The tank leaching test indicated that the release mechanism of trance elements (Cr, As, Zn, Cd, Pb and Ni) was mainly controlled by diffusion. This study provides useful knowledge for decreasing the volatilization and leaching of HMs from sintered bricks prepared using hazardous waste.

Cement encapsulation processes to mitigate the risks posed by different types of antimony-bearing mine waste

In this study cement encapsulation processes of different types of mine waste generated from the exploitation of Sb ore deposits were evaluated as a way to manage them and avoid further environmental pollution and the negative impact on surrounding ecosystems. For this purpose, Sb-bearing mine waste rocks, mine tailings, and smelting waste were subjected to cementation processes using Portland cement/calcium hydroxide as binder and different binder:mine waste ratios (10:90–80:20 wt%). The encapsulated materials were characterized for their mechanical behavior (compressive strength test), leaching properties (batch shaking and tank leaching tests), and mineralogical and chemical composition by X-ray powder diffraction, scanning electron microscopy, and electron microprobe analysis. A binder:mine waste ratio of 40:60 wt% was found appropriate to decrease the leachable Sb concentrations at levels below the limit for acceptance at non-hazardous waste landfills. Diffusion was the main mechanism controlling Sb leaching. The obtained effective diffusion coefficients and developed compressive strengths indicate that the encapsulated materials were suitable for disposal. Therefore, according to their leaching and strength characteristics, the encapsulated mine wastes derived using the indicated conditions could be deposited at landfills for non-hazardous waste, thus minimizing the environmental hazards caused by their accumulation in the mine surrounding areas. Additionally, according to the Dutch legislation on the use of waste materials in the built sector, some formulations of encapsulated mine tailings already met the Sb leaching requirement for open (un-insulated) construction applications. Therefore, Sb-bearing mine wastes, especially mine tailings, also present a great potential to be recycled as substitutes for natural aggregates in concrete in construction applications. Antimony was mostly preserved in the original Sb-bearing phases [Fe and Sb (oxyhydr)oxides and tripuhyite] after the encapsulation processes. Of compounds resulting from the hydration of Portland cement, C-(A)-S-H phases predominated, having an important role in attenuating the Sb release from the different types of mine waste; average Sb2O5 contents of 0.12–0.31 wt% were found in C-(A)-S-H phases.

Assessment of metal leaching from rediset-polymer modified asphalt binder on groundwater and soil contamination

Road pavement is a structure that expose to various climate conditions. To make it more durable, modification of asphalt binder with polymer is a popular option. However, to maintain the environmental sustainability, the mixing and compaction temperature needs to be reduced. Warm Mix Asphalt additive had been widely used for this purpose. In this research, the impact of a polymer modified asphalt binder, PG76 together with a chemical WMA additive, Rediset on groundwater and soil contamination was investigated. The effect of Rediset on PG76 in terms of viscosity and activation energy was also studied via the rotational viscosity test. Even though it was found that Rediset might affect the viscosity of PG76, the activation energy shows independent values. ATR-FTIR was employed to understand the reaction between these two substance. It was found that there had been no chemical reaction between PG76 and Rediset. As a complementary, AFM was utilised to observe the surface characteristics at micro-scale. It appeared that Rediset did contribute to the binder’s surface morphology. Finally, the modified tank leaching test together with analysis by ICP-MS, discovered that after 64 days submerged under flood, Rediset-PG76 had no effect on the adjacent water source and soil.

Feasibility and Environmental Compatibility of Concrete using Chromium Bearing Wastewater

The effluents of chrome plating industry seepage contain toxic hexavalent chromium generally in the range of 100 to 300 mg/L. The said values of chromium are not advisable to dispose to surface water bodies or land and the treatment process of this wastewater is quite expensive. Herein, we found a course of action to reuse the wastewater in cement matrix in manufacturing concrete work. The M-30 grade concrete samples were casted with portland slag cement (PSC) at wastewater to binder ratio of 0.45. The technical compatibility of concrete specimen i.e. the chromium immobilization and other properties are well satisfied nevertheless a small decrease in hardened concrete values also observed. XRD study revealed that the hydration product Ca(OH)2 is replaced by more insoluble CaCrO4. Scanning electron microscopy study (SEM) with energy dispersive spectrum (EDS) study exhibited the immobilization of chromium and quantification of chromium content. The mortar samples from concrete after 56 days of air curing were subjected to toxicity characteristic leaching procedure (TCLP) test at pH 2.88. In addition, two days’ short tank leaching test was conducted with the concrete samples as a whole. The leachability of toxic Cr6+ found in the range 0.03-0.09 mg/L and the total chromium (TCr) values in the range 0.12 -0.17 mg/L, which are less than discharge standard as per EP Act (1986), India. All these leaching test results comply with the discharge norms to land and inland surface water, respectively. Thus, the concrete specimens using aforesaid wastewater satisfy the technical aspects and fulfil the environmental requirement.

Mechanical and vegetation performance of porous concrete with recycled aggregate in riparian buffer area

This study is to evaluate the potential application of porous concrete with recycled coarse aggregate (RA) in riparian buffer area from two aspects: mechanical behaviour and vegetation performance. The effect of curing duration, RA grading, water/cement ratio (W/C) and cement paste/RA ratio (CP/RA) on the porosity and strength of RA porous concrete were determined by effective porosity and compressive strength tests, followed with evaluating the durability by wetting-drying (W-D) cycle tests. The vegetation performance of the porous concrete was evaluated, and then a tank leaching test was carried out to investigate the absorption capacity for total nitrogen (T-N) and total phosphorus (T-P). The results show that the compressive strength strongly depends on the bonding capacity among RA grains and slightly depends on RA grading; CP/RA ratio has a greater effect on effective porosity than other variables since diluted cement paste is more liable to fill the pores in the concrete; the mass transport (MT) values when suffering different W-D regimes ranges from 0.98 to 2.36%, indicating that porous concrete can maintain the structural integrity. Porous concrete with the RA grading (20–25 mm) is more suitable for vegetation growth than other grading, and incorporating with plants exhibits a considerable removal efficiency for T-N and T-P in wastewater, with maximum values of 59.82% and 61.99%, respectively. In general, the porous concrete with RA investigated in this research can offer a prominent technical advantage when applied in riparian buffer zones considering its structural improvement and reducing environmental load.

Physical, leaching, and toxicity characteristics of PG76 binder modified with Rediset

Asphalt binder, as one of pavement component is exposed to heat and rainfall. Polymer modified asphalt binder is a good alternative to withstand the weather in tropical countries. By utilizing warm mix asphalt additive, the high compacting and mixing temperature can be reduced. However, the impact to the environment and its characteristic towards high temperature need to be evaluated before putting it to use. In the study, the physical properties, thermal characteristics, and leaching and toxicity of PG76 incorporated with Rediset LQ were investigated. The Tank Leaching Test was carried out to mimic the worst scenario of flood event effect on the asphalt binder. The results of physical tests denote that the new material has relative consistency while the thermal analysis indicates that the materials are stable beyond their mixing and compaction temperature. The decomposition starts at temperature > 360°C and ends at temperature <500°C for all samples. The tank leaching test also found that the materials are safe to be used as pavement material because the heavy metal elements from the leachate are below the maximum allowable volume by the World Health Organization and the United States Environmental Protection Agency.

Valorization of incinerator bottom ash for the production of resource-efficient eco-friendly concrete: Performance and toxicological characterization

In recent times, the quantity of wastes generated from industries, hospitals, construction sites etc. is perpetually increasing from year to year. Producing concrete utilizing waste or discarded materials as a partial replacement to fine or coarse aggregates is one among the effective ways of waste utilization. The disposal of incinerator bottom ash usually produced by the incineration of inorganic constituents of the municipal solid wastes (MSW) in an eco-friendly way is one of the issues of concern, globally. By the way, the present study is related to the utilization of MSW incinerator bottom ash and recycled demolition waste aggregate as partial replacement materials for fine and coarse aggregate, respectively to produce eco-friendly concrete. This study adopted an innovative pretreatment technique for stabilizing the MSW incinerator bottom ash. Five distinct M20 grade concrete mixes were produced with different proportions of fine aggregate, MSW incinerator bottom ash, coarse aggregate, and recycled demolition waste aggregate along with cement and water. The incinerator bottom ash was replaced at 5% and 10% quantities with fine aggregate and the recycled demolition waste aggregate was replaced at 40% and 60% of the weight of the coarse aggregate. The strength and durability properties of the M20 grade concrete were analyzed. It was noticed that the strength and durability properties of the eco-friendly concrete specimens produced by incorporating 5% - incinerator bottom ash and 40% - recycled demolition waste aggregate were superior to that of the control mix concrete. Laboratory tank leaching tests showed that the eco-friendly concrete do not pose any significant environmental hazard. Furthermore, the microstructural analysis through scanning electron microscope (SEM) images, revealed dense aggregate paste matrix interfaces with less micro-pores and insignificant micro-cracks due to the incorporation of incinerator bottom ash as a partial replacement to the fine aggregate.

Leaching of As and Se from coal fly ash: fundamental study for coal fly ash recycling.

Coal fly ash (CFA) is a useful recycled resource for uses such as cement raw material. To manage and evaluate safety for effective utilization of CFA, the leaching concentration and amounts of toxic elements in CFA need to be determined. In this study, 38 types of CFA and aged CFA generated in Japan were used to measure the occurrence and leaching concentration range of As and Se. In addition, the leaching characteristics over the long term were examined using statistical analysis. Leaching concentrations of As and Se from CFAs were in the range of 0.001-0.163mg/L (average: 0.025mg/L, median: 0.014mg/L) and 0.001-0.189mg/L (average: 0.071mg/L, median: 0.055mg/L), respectively. In general, the concentrations of aged CFAs were less than those of the CFAs with a few exceptions. Leaching concentrations of As and Se in the tank leaching test changed with time, and As and Se concentrations in the dispersions increased with stirring time. In contrast, pH of the dispersion decreased with time. The relation between As or Se and CFA factors showed that As or Se and pH or Ca were highly correlated. However, in aged CFAs for long-term use, the correlation coefficient for the relation between As and other factors was low while that for Se-S was high. Considering the effective utilization of CFA as a long-term recyclable resource, the leaching processes of As and Se in CFA would change with time depending on the environmental conditions.

A comparison study of three fluxing agents in promoting properties and environmental safety of bricks incorporating hazardous waste

The incorporation of hazardous solid waste in fired bricks fabrication is a viable way. However, the physical and mechanical properties of products were negatively influenced due to the involvement of hazardous solid waste. Three fluxing agents, waste glass powder (WGP), Na-feldspar and K-feldspar, were introduced in this study to eliminate these negative influences. Physical and mechanical properties were tested by standard method. Microstructure and pore structure of bricks were conducted by Scanning Electron Microscopy (SEM) and nitrogen adsorption and desorption isotherm. The change in mineral phase was detected by X-Ray Diffraction (XRD). The leaching toxicity of heavy metals were carried out by Toxicity Characteristic Leaching Procedure (TCLP) and Netherlands tank leaching test . The introduction of fluxing agents can greatly promote effectively compressive strength and decline water absorption. When 30 wt% (weight percent) of fluxing agents are added, water absorption reduced by more than 50%, and compressive strength increased by more than one time. XRD and SEM analysis showed that fluxing agents can promote the formation of glass-ceramic phase, which were mainly formed by the self-melting reaction of fluxing agents and the interaction with silicon-aluminium oxides. These dense glass phases could reduce the porosity and promote the compactness of microstructure. The formation of glass-ceramic phases could also reduce the leachability risk of heavy metals. Combing with properties of brick and price of fluxing agents, WGP is considered to be more suitable for improving properties of fired bricks containing hazardous waste . This study could provide some useful parameters and knowledge for improving properties and leaching toxicity risk when hazardous wastes were utilized in the production of fired brick. Fluxing agents can reduce water absorption substantially. Fluxing agents can promote compressive strength remarkably. Microstructure become homogeneous and dense due to fluxing agents Fluxing agents can decrease leachability of heavy metals

Assessment of the long-term leaching characteristics of cement-slag stabilized/solidified contaminated sediment

The use of stabilized/solidified (S/S) soils and sediments as sustainable construction materials is a global concern due to the potential risk of contaminant leaching including potentially toxic elements. The long-term leachability of four metals (Zn, Pb, Cd and As) in sediments mixed with OPC (Ordinary Portland Cement) and OPC/GGBS (Ground Granulated Blast Furnace Slag) binders were investigated through a combination of tank leaching tests and kinetic leaching models, with varying ranges of curing ages and ambient pH. The leaching data revealed that both binder compositions offer an excellent immobilization capacity for the four metals, while their releases are strongly pH-dependent and are a complex function of curing time. The partial replacement of OPC by GGBS is more effective for fixing Zn and As at pH of 1, Pb at pH of 7, Zn and Pb at pH of 10. Controlling leaching mechanisms and leachability indices were determined using nonlinear regression analysis and kinetic leaching models. The first-order diffusion model (FRDM) was the most applicable model for describing the leaching characteristics of these metals under the investigated cases, the leaching rate is controlled by surface wash-off initially and then by diffusion. The leachability indices indicate that the cement-slag S/S sediment can be regarded as an environmentally sustainable material with potential beneficial uses in construction.

Stabilization/solidification and recycling of sediment from Taihu Lake in China: Engineering behavior and environmental impact

Investigations of stabilized/solidified sediment (S/S sediment) by simulated field-construction processes (crushing and filling) are fundamental to evaluating the potential reuse as fill materials. A series of tests were conducted on the samples prepared from S/S sediment grains (SG), which was obtained by crushing the cement treated sediment. By sampling the SG with different field-curing durations (t1: 28, 35, 56 and 98 days) and measuring them by unconfined compressive strength (UCS) tests, the effect of t1 on the UCS was investigated. By continually curing the samples prepared from the SG with 28 field-curing days in laboratory for an additional 7, 28, 35 and 70 days (t2) and subjecting them to UCS and tank leaching tests with different ambient (leachate) pH values (1, 4, 7, 10 and 14), the effect of t2 and ambient pH was evaluated. Increasing t1 and t2 was found to significantly influence the strength of SG, which highlights the importance of an appropriate curing period. The releases of the metals (As, Cr, Cu, Zn, Pb, Ni, and Hg) in the SG exhibited a strongly pH-dependence but less correlation with t2. Neutral conditions (pH = 7) offered the best immobilization capacity for Cu; As, Cr, Ni and Zn exhibited the lowest release at pH = 10; the release of Pb decreased moderately with increasing pH. The S/S sediment complied with the acceptance criteria in terms of metal release and can be regarded as an environmentally friendly fill material. The results highlight the technical feasibility of stabilized sediment recycling in aquatic environment projects.

Dredged marine sediments stabilized/solidified with cement and GGBS: Factors affecting mechanical behaviour and leachability

Management strategies for the safe disposal of contaminated dredged marine sediment constitute a global-scale environmental issue. The stabilization/solidification method was investigated as a sustainable approach to the recycling of the sediment as a construction material. A systematic study of the factors affecting the mechanical performance and contaminant release was performed. The physico-chemical variables selected to assess the potential re-use of the sediment treated with Ordinary Portland cement (OPC) and Ground Granulated Blast Furnace Slag (GGBS) in an aquatic environment were: curing duration (7, 28, 56 and 98 days), curing temperature (5, 20 and 40 °C) and ambient (leachate) pH (1, 4, 7 and 10). Unconfined compressive strength (UCS) tests were conducted and extended-duration tank leaching tests were used to characterize the long-term leaching of Al, Cr, Mn, Fe, Ni, Cu, Zn, As, Cd, Ba, Pb. The results showed that S/S methods provide excellent immobilization of metals in marine sediment at a pH range of 4 to 10. Immobilization efficiencies of >99.9% for Mn, Fe, Zn, As, Ba, Pb and >97.8% for Al, Cu and Zn are reported over 100 days. GGBS replacement is an effective way to further improve sediment properties by enhancing strength, mitigating sediment alkalization and offering a better immobilization capacity for Fe, Ni and Zn. The release of metals (Al, Mn, Cu, As, Ba and Pb) was strongly associated with a coupling effect of the physico-chemical factors, with metal-specific responses to curing temperature, curing duration and pH. Mn mobility showed a dramatic sensitivity to ambient pH while Ba was less pH-dependent. Al release is related to strength and leached out by dissolution in all situations considered. Considering that dredged marine sediments may contain multiple metal contaminants which exhibit individual responses to remediation, treatment with GGBS may be considered a potentially suitable management option.

Environmental behavior of waste rocks based concrete: Leaching performance assessment

The reuse of mine waste rocks as construction material is an innovative and sustainable management technique that can lower their surface disposal, mitigate their environmental impacts and provide opportunity to conceive economic benefits. However, the implementation of this approach is still limited due principally to insufficient knowledge on environmental behavior of mine wastes-based products. This paper aims in investigating these issues by assessing the leaching behavior of two low sulfide-mining waste rocks suitable for concrete production. Concentrations of inorganic contaminants released from single waste rocks were measured by means of weathering cell, CTEU-9, TCLP and SPLP tests. Compressive strength and immobilization performance of obtained concretes based on these waste rocks were assessed. The results of humidity cell tests indicated that waste rock with higher sulfur content (0.47 wt%) and lower carbon content (0.26 wt%) did not present an acid generating potential according the Quebec environmental regulation. Those of TCLP, SPLP and CTEU-9 batch tests showed a concentration of contaminants in leachate solutions from waste rocks below the standardized limits fixed by the Environmental Protection Agency. Concretes made using these waste rocks as aggregates exhibited a suitable compressive strength. Concentration of heavy metals and sulphates released from concretes using tank-leaching test were under the limit requirements fixed by the Soil Quality Decree.

Slurry Preparation Effects on the Cemented Phosphogypsum Backfill through an Orthogonal Experiment

The cemented phosphogypsum (PG) backfill technique provides a new method for massive consumption of PG, and therefore alleviating the environmental pollution of PG. This study considered the effects of slurry preparation on the performance of cemented PG backfill. A L16(44) orthogonal experiment was designed to analyze four factors, namely the solid content, phosphogypsum-to-binder ratio (PG/B ratio), stirring time and stirring speed, with each factor having four levels. According to the range analysis, the solid content played the dominant role in controlling the bleeding rate, while the setting times strongly depended on the PG/B ratio. In terms of strength development of the backfill, the PG/B ratio was shown to be the most significant factor determining the unconfined compressive strength (UCS), followed by the solid content, stirring time and stirring speed. Furthermore, the results showed that the slurry preparation affected the environmental behavior of impurities that originated in PG. By analyzing the concentrations of impurities in the bleeding water of the slurry as well as the leachates of the tank leaching test, the results showed that the release of F− and SO42− was aggravated clearly with the increase in the PG/B ratio, while the release of PO43− always remained at relatively low levels.