Performance of waste-based amendments to reduce metal release from mine tailings: One-year leaching behaviour

Revealing the release and migration mechanism of heavy metals in typical carbonate tailings, East China

Refining the occurrence characteristics of tailings hazardous materials at source is of great importance for pollution management and ecological reclamation. However, the release and transport of heavy metals (HMs) from tailings under rainfall drenching in simulated real-world environments is less well portrayed, particularly highlighting the inherent neutralisation in tailings wastes under superimposed dynamic conditions. In this study, dynamic leaching columns simulating actual conditions were used to observe the release and transport of HMs from tailings under acid rainfall infiltration at spatial and temporal scales. The release rate of trace elements (e.g., As, Cr, Ni, Pb, Cd) is high. Neutralisation in the presence of carbonate rocks in the gangue reduces HMs release intensity from tailings with high heavy metal content, along with the precipitation of iron oxides and chromium-bearing minerals, etc. In addition, the vertical differentiation of HMs is more relevant to physical processes. In the absence of carbonate rocks in gangue, the lowest pH value is reached within 1.2 h after acid rain infiltrates the tailings. At the same time, Cu, Zn and Cd are released significantly from the minerals at the superficial level. The release of As(III) is mainly concentrated in the early and late stages of water-rock contact.

Solidification and stabilization of Pb-Zn mine tailing with municipal solid waste incineration fly ash and ground granulated blast-furnace slag for unfired brick fabrication

The mismanaged and abandoned mine tailings are an important source of heavy metal pollution in the mining regions, and there is a significant need to develop technically, environmentally, and economically feasible and sustainable solutions to manage them. This study explored the solidification and stabilization of the tailing from an abandoned Pb-Zn mine using municipal solid waste incineration fly ash (MSWIFA) blended with ground granulated blast-furnace slag (GGBFS) for fabricating unfired bricks, and systematically characterized the products' mechanical and environmental performance. Various hydration products, such as ettringite, portlandite, and hydrotalcite, were formed in the unfired bricks in the solidification and stabilization process, which enhance the physical strength of unfired bricks and help immobilize the heavy metals. Slaking treatment of MSWIFA significantly increased the mechanical strength, reduced the water absorption, and improved the durability of unfired bricks, with the product prepared from MSWIFA with 7-day slaking exhibiting the highest unconfined compressive strength (12.3 MPa) after 56 days of curing. The concentrations of As (0.35-1.49 μg/L), Cd (0.35-0.70 μg/L), Cr (1.38-9.40 μg/L), Cu (2.28-5.87 μg/L), Ni (0.16-2.24 μg/L), Pb (0.16-59.80 μg/L), and Zn (1.60-10.80 μg/L) in the leachates of unfired bricks were below the relevant regulatory limits for surface water and groundwater. Converting the mine tailing (with MSWIFA and GGBFS) to different types of unfired bricks could yield economic payback in the range of 283.7-306.5 Yuan per ton. Replacing cement with MSWIFA blended with GGBFS in the solidification and stabilization treatment could save about 0.15 ton of cement per ton of mine tailing disposed, which avoids significant energy use and carbon dioxide emissions. These findings demonstrate that utilization of mine tailings and industrial wastes to fabricate unfired bricks is a promising way of reusing such wastes and controlling the associated pollution, which also brings significant economic benefit and improves environmental sustainability.

An ecological remediation model combining optimal substrate amelioration and native hyperaccumulator colonization in non-ferrous metal tailings pond

The vegetation deterioration and pollution expansion from non-ferrous metal tailings pond have been found in many countries leading to water soil erosion and human health risk. Conventional ecological remediation technologies of mine tailings such as capping were costly and elusive. This study provided an economic and effective model as an alternative by substrate amelioration and vegetation restoration. A field experiment was carried out on a silver tailings pond in southwest China. Tailings substrate was ameliorated by adding organic matter (decomposed chicken manure, DCM), structural conditioner (polyacrylamide, PAM), water-retaining agent (acrylic acid-bentonite water-retaining agent, AAB), and heavy metal immobilizer (biofuel ash, BFA), which were optimized by laboratory experiment. Native heavy metal hyperaccumulator, Bidens pilosa, was colonized. Vegetation coverage and plant height of Bidens pilosa reached about 80% and over 30 cm respectively after 3 months, and the turbidity of tailings leaching solution decreased by 60%. The practice showed that the proportion of available heavy metals in tailings substrate was significantly lower than that in the soil surrounding mining area. Immobilization didn't have stabilization effect on Cd, Zn, and Pb, and As was only 0.002%, phytoremediation had stabilization effect of Cd, Zn, As, and Pb were 2.5-3.5%, 1-2%, 0.25-0.5%, and 0.25-0.75%. Phytoremediation was more effective significantly in controlling heavy metal pollution risk of tailings than immobilization. These results provided a new ecological remediation OSA-NHC model, meaning a combination of optimal substrate amelioration and native hyperaccumulator colonization, which could achieve vegetation restoration and augment heavy metal pollution control in non-ferrous metal tailings pond.

Temporal evolution of surface and sub-surface geochemistry and microbial communities of Pb-rich mine tailings during phytostabilization: A one-year pilot-scale study

Old mine waste repositories can present health and/or environmental issues linked to their erosion, inducing dissemination of metals and metalloids in air and water that can be attenuated through phytostabilization. Here, the effect of this widespread phytomanagement option on the biogeochemistry of a Pb-rich mine waste was evaluated with a laboratory pilot-scale experiment giving access to the non-saturated and saturated zones below the rhizosphere compartment. Amendment of the tailings surface with biochar, manure and iron-oxide-rich ochre promoted growth of the seeded Agrostis capillaris plants. These events were accompanied by an increase of pH and a decrease of Pb concentration in pore water of the surface layer, and by a transient increase of Pb, Zn, and Ba concentrations in the deeper saturated levels. Macroscopic and microscopic observations (SEM) suggest that Pb was immobilized in A. capillaris rhizosphere through mechanical entrapment of tailing particles. Microbial taxonomic and metabolic diversities increased in the amended phytostabilized surface levels, with a rise of the proportion of heterotrophic micro-organisms. Below the surface, a transient modification of microbial communities was observed in the non-saturated and saturated levels, however 11 months after seeding, the prokaryotic community of the deepest saturated zone was close to that of the initial tailings. pH and water saturation seemed to be the main parameters driving prokaryotic communities' structures. Results obtained at pilot-scale will help to precisely evaluate the impacts of phytostabilization on the temporal evolution of reactions driving the fate of pollutants inside the tailings dumps.

Leaching of heavy metals from lead-zinc mine tailings and the subsequent migration and transformation characteristics in paddy soil

The leaching of heavy metals (HMs) from lead-zinc mine tailings caused by natural precipitation and the subsequent migration and transformation characteristics in paddy soil were investigated using simulative experiments. The contents of HMs in the leachate from lead-zinc mine tailings increased with the increasing of liquid-to-solid ratio. Significant differences of contents under the same rainfall were found among different HMs (P < 0.01). The increasing rates of the concentrations for Mn and Zn in leachate were much higher than the other selected HMs. The leaching results of all HMs were well fitted by the DoseResp equation, indicating that the leaching processes are controlled by multiple factors. When the paddy soil was exposed to lead-zinc mine tailings, the HMs could accumulate significantly in the paddy soil, and their contents increased with the simulated time. The average vertical migration rates (mg kg^-1 cm^-1 d^-1) of HMs in the paddy soil during the four months was ranked in the order of Zn (9.0✕10^-2) > Mn (8.1✕10^-2) > Cu (1.8✕10^-2) > Pb (1.6✕10^-2) > Cd (2.7✕10^-4) > As (2.4✕10^-4). Compared with the other HMs, Mn and Zn can be more easily leached from lead-zinc mine tailings, then migrate into deeper layers in paddy soil. The proportions in five chemical fractions of HMs varied significantly with the impact of lead-zinc mine tailings. The Zn, Cu, and As were mainly presented in residual fraction, while Pb, Mn, and Cd were mainly presented in carbonate-bound, Fe/Mn oxides-bound, and exchangeable fractions, respectively. The risk assessment code results showed that Zn, Mn, Cu, and As posed medium risk, while Pb and Cd posed an extremely high risk to the paddy soil environment. It's found that lead-zinc mine tailings could significantly enhance the ecological risk associated with HMs in the paddy soil.

Treatment of Soil Contaminated by Mining Activities to Prevent Contamination by Encapsulation in Ceramic Construction Materials

Mining is an essential activity for obtaining materials necessary for the well-being and development of society. However, this activity produces important environmental impacts that must be controlled. More specifically, there are different soils near new or abandoned mining productions that have been contaminated with potentially toxic elements, and currently represent an important environmental problem. In this research, a contaminated soil from the mining district of Linares was studied for its use as a raw material for the conforming of ceramic materials, bricks, dedicated to construction. Firstly, the contaminated soil was chemically and physically characterized in order to evaluate its suitability. Subsequently, different families of samples were conformed with different percentages of clay and contaminated soil. Finally, the conformed ceramics were physically and mechanically characterized to examine the variation produced in the ceramic material by the incorporation of the contaminated soil. In addition, in this research, leachate tests were performed according to the TCLP method determining whether encapsulation of potentially toxic elements in the soil occurs. The results showed that all families of ceramic materials have acceptable physical properties, with a soil percentage of less than 80% being acceptable to obtain adequate mechanical properties and a maximum of 70% of contaminated soil to obtain acceptable leachate according to EPA regulations. Therefore, the maximum percentage of contaminated soil that can be incorporated into the ceramic material is 70% in order to comply with all standards. Consequently, this research not only avoids the contamination that contaminated soil can produce, but also valorizes this element as a raw material for new materials, avoiding the extraction of clay and reducing the environmental impact.

Abandoned Mine Lands Reclamation by Plant Remediation Technologies

Abandoned mine lands (AMLs), which are considered some of the most dangerous anthropogenic activities in the world, are a source of hazards relating to potentially toxic elements (PTEs). Traditional reclamation techniques, which are expensive, time-consuming and not well accepted by the general public, cannot be used on a large scale. However, plant-based techniques have gained acceptance as an environmentally friendly alternative over the last 20 years. Plants can be used in AMLs for PTE phytoextraction, phytostabilization, and phytovolatilization. We reviewed these phytoremediation techniques, paying particular attention to the selection of appropriate plants in each case. In order to assess the suitability of plants for phytoremediation purposes, the accumulation capacity and tolerance mechanisms of PTEs was described. We also compiled a collection of interesting actual examples of AML phytoremediation. On-site studies have shown positive results in terms of soil quality improvement, reduced PTE bioavailability, and increased biodiversity. However, phytoremediation strategies need to better characterize potential plant candidates in order to improve PTE extraction and to reduce the negative impact on AMLs.

Laboratory Study on the Effectiveness of Limestone and Cementitious Industrial Products for Acid Mine Drainage Remediation

Acid mine tailings may affect several environmental matrices. Here, we aimed to stabilize acid-generated mine tailings using several alkaline and cementitious amendments, which were tested in columns for 361 days. The alkaline amendments consisted of 10 and 20 wt.% limestone, while the cementitious amendments consisted of different binders at a total dosage of 5 wt.% binder. The different formulations for the cementitious amendments were: 50% Kruger fly ash and 50% class F fly ash; 20% ordinary Portland cement, 40% Kruger fly ash, and 40% class F fly ash; 80% ordinary Portland cement and 20% Kruger fly ash; and 20% ordinary Portland cement, 40% Kruger fly ash, and 40% fly ash. Kinetic testing on the amendment formulations showed that the pH values increased from <2.5 to circumneutral values (~7.5). The mobility of various chemical species was greatly reduced. Cumulative Fe released from the unamended tailings was ~342.5 mg/kg, and was <22 mg/kg for the amended tailings. The main mechanisms responsible for metal(loid) immobilization were the precipitation of secondary phases, such as Fe-oxyhydroxides, physical trapping, and tailing impermeabilization.

From wastes to functions: A paper mill sludge-based calcium-containing porous biochar adsorbent for phosphorus removal

With the increased awareness of reusing solid wastes for higher sustainability and the concern of water pollution associated with phosphorus over-emission, there are strong interests in developing solid waste based adsorbents for purifying phosphorus-containing wastewater. As a rich calcium resource, paper mill sludge (i.e., a major solid waste from pulping industry) can be used as phosphorus removal adsorbent after calcination. Thus, in this work, a simple and clean thermally treating route has been proposed for preparing calcium-containing biochar from paper mill sludge. The effect of the physicochemical properties of paper mill sludge and its carbonization condition on phosphorus adsorption has been analyzed. Moreover, the influence of some key adsorption parameters, e.g., biochar dosage, initial pH of solution, co-existing anions, initial phosphorus concentration and contact time has also been investigated. The results showed that the phosphorus adsorption data could be fitted well with pseudo-second-order kinetic and Langmuir isothermal models. The calculated maximum adsorption capacity of the as-prepared optimal calcium-containing biochar could reach to 68.49 mg·g^-1 at 25 °C. Combined with the characterization results, it can be reasonably inferred that the adsorption process was chemisorption-dominated. Lastly, the application of this spent adsorbent in agriculture field has also been discussed. In brief, this work provided a feasible strategy for converting paper mill solid waste to an environmental functional material (i.e., calcium-rich biochar) for remediation of eutrophic water.

Performance of the emerging biochar on the stabilization of potentially toxic metals in smelter- and mining-contaminated soils

Soil potentially toxic metals (PTMs) pollution caused by anthropogenic activities has become serious concern with respect to the crop safety production. In this study, an emerging biochar derived from kiwi pruning branches waste was employed as amendment aiming to evaluate its remediation potential on smelter- and mining-contaminated soils. The effect of biochar on the soil physicochemical properties, leachability, and chemical fractions acted on stabilization practice of PTMs in soil was investigated. The results showed that the addition of biochar increased the soil pH, cation exchange capacity, organic matter, and enzymatic activities (dehydrogenase, urease, and sucrase) but reduced the extraction toxicity of PTMs in both smelter (Fengxian, FX) and mining (Tongguan, TG) soils. The fraction analysis showed that the maximum reduction of exchangeable fraction of Cd, Zn, and Pb in the 4% biochar amended soils decreased by 11.1, 13.3, and 24.7% in FX soil and 7.67, 22.8, and 7.89% in TG soil, respectively, in comparison with to control (no biochar added). Additionally, the residual fraction of Cd, Zn, and Pb increased by 55.9, 7.14, and 11.0% in FX soil and 23.7, 5.86, and 10.0% in TG soil, respectively. The further greenhouse experiment showed that the Indian mustard (Brassica juncea) production increased with the increasing application dosages of biochar, while the PTMs uptakes in plant notably decreased after amendments. Conversion of kiwi pruning branches waste into emerging biochar benefits the agricultural waste recycling utilization and enhances PTMs-contaminated soil remediation in practice. Graphical abstract.

Barriers for plant establishment in the abandoned tailings of Nacozari, Sonora, Mexico: the influence of compost addition on seedling performance and tailing properties

Past mining activities have left a legacy of abandoned mine tailing deposits whose metal contaminants poses serious risks to ecosystems and human health. While the development of a vegetated cover in mine tailings can help in mitigating these risks, the local factors limiting plant establishment in these sites are not well understood, restricting phytostabilization efforts. Here, we explore some of the barriers that limit seedling establishment of two species (Vachellia farnesiana and Prosopis velutina) in a mine tailing deposit located in Nacozari, Sonora, Mexico, and assess whether compost addition can help in overcoming these barriers in pot and field experiments. Our field observations found 20 times more carbon and at least 4 times more nitrogen concentration in areas under vegetated patches than in non-vegetated areas, while a previous study found no difference in metal concentrations and other physicochemical parameters. This suggests that organic matter and nutrients are a major limitation for plant establishment. In agreement with this, species failed to establish without compost addition in the field experiment. Compost addition also had a positive effect on biomass accumulation, pH and microbial activity, but increased the substrate soluble concentration of As, Cu, and Zn. Nonetheless, only Cu, K, and Mo in P. velutina accumulated in tissues at levels considered toxic for animal consumption. Our study documents that compost addition facilitated plant establishment for the phytostabilization of mine tailings and help to prevent the dispersion of most metal contaminants via animal consumption. We encourage the use of complementary strategies to minimize the risk of dispersion of metal contaminants.

A new ranking scale for assessing leaching potential pollution from abandoned mining wastes based on the Mexican official leaching test

Potentially toxic elements (PTEs) present in abandoned mining wastes (AMW) are of great concern because of potential risks to human health and ecosystems. Indices of contamination (IC) applied to mining wastes are calculated using the total concentration of PTEs and comparing them with regional geochemical backgrounds. However, determining the total content of heavy metals is insufficient to assess the hazard of mining wastes. Therefore, in addition to total concentration, the potential risk is also evaluated through water mobility of elements. Accordingly, leaching procedures are useful tools for the geochemical characterization of soluble constituents that are mobilized. In this study, the solubility of PTEs from different types of mining wastes is comparatively assessed using three standard leaching methods (European; U.S. Geological Survey and; Mexican). The Hazard Average Quotient (HAQ) was calculated to assess the potential Toxicity Factor (TF). TF is an indicator of the relative potential toxicity of wastes and is the basis for the classification of AMW. A comparative assessment provides evidence that there are no statistically significant differences in PTEs solubility by the three leaching methods and it was also found that the pH of the eluates was dictated by the type of waste. Results suggest that the IC gives an indicator of the potential contamination of soils and sediments by erosive processes, or a long-term measure, whereas TF assesses the possibility of contaminating water in the short term. The most significant finding is the new ranking scale of TF, as a function of HAQ, applied to the Mexican standard leaching test. This factor, together with other considerations relating to risk-generating processes, might then be applied in places having large amounts of recorded AMW, such as the Iberian Peninsula and Latin America, where effective management is required to rank sites, based on preliminary environmental and human risk assessment.

The impact of natural weathering and mining on heavy metal accumulation in the karst areas of the Pearl River Basin, China

This paper presents the heavy metal content in river water, sediment and bedrock in the karst area of the Pearl River Basin in China to evaluate the long-term impact of natural weathering and mining on the ecological environment. The results show that Cd and As is 2-3 times more enriched within the carbonate bedrock of the Pearl River Basin compared to the upper continental crust (UCC), which is indicative of high geological background values. Within the river water of the upper reaches of the Diaojiang River (a tributary of the Pearl River), which flows through the Dachang super-large orefield, Zn, As, Cd and Sb exceeds the environmental quality standards for surface water (WQS) by more than an order of magnitude. Among these, Zn and Cd sharply decreases to within the WQS in the lower reaches of the river, but the content of As and Sb in the estuary is still several times higher than the WQS. Cd in the sediments of the small carbonate watersheds and in the mainstream of the Pearl River only present a low-moderate ecological risk. In contrast, severe heavy metal pollution of the sediments of the Diaojiang River Basin is observed. Even in the lower reaches, remote from the mining area, the content of Pb, Zn, As and Cd in the sediments is still two orders of magnitude higher than the soil background values. The content of both Cd and As presents a very high ecological risk, indicating that under the cumulative effect of high geological background values and mining, full restoration of the ecological environment in the Diaojiang River Basin is a complex and long-term process.

Leaching of heavy metals from abandoned mine tailings brought by precipitation and the associated environmental impact

Abandoned tailings are one of the most important sources of heavy metal pollution in the areas surrounding mining districts, and significant leaching of heavy metals could be brought by precipitation. This study investigated the leaching of heavy metals from the tailings of a small-scale abandoned polymetallic mine in south China by rainwater with batch and column tests and evaluated the associated environmental impact. The mean contents of Cr, Ni, Cu, Zn, As, Cd, and Pb in the un-weathered mine tailings were 1.46×10², 3.11×10², 4.10×10³, 2.18×10⁴, 2.82×10², 5.65×10², and 8.74×10³mg/kg, respectively, and appreciable fractions of Cd, Zn, Cu, and Cr in the tailings were present in the acid soluble form. Batch and column leaching tests consistently showed that significant quantities of heavy metals could be released from the mine tailings. Based on the results of column leaching tests, it was estimated that the average fluxes of Cr, Ni, Cu, Zn, As, Cd, and Pb from the mine tailings at the studied mining district leached by precipitation were 3.20, 38.3, 12.5, 1.52×10⁴, 104, 1.08, and 9.26g/ha/yr, respectively. The metal-rich tailing leachate would impact the quality of surface water and soils downhill of the mining district, and pose significant potential ecological risk to the farmland soils, which are irrigated by local surface water. These findings indicate the importance of tailings as a source of heavy metals in the mining districts of south China with heavy precipitation, as well as the need for mitigating the releases of heavy metals and the associated environmental impact from abandoned mine tailings.

In Situ Effectiveness of Alkaline and Cementitious Amendments to Stabilize Oxidized Acid-Generating Tailings

This study investigates the effectiveness of alkaline and cementitious additives in the in situ stabilization of localized acid-generating tailings from a closed gold mine in Abitibi–Témiscamingue, Québec (Eagle/Telbel mine site). Five field cells (including one control) were constructed and equipped with mechanisms for collecting vertical water infiltration and surface runoff. The five cells included: (C1) Control cell; (C2) 5 wt % limestone amendment; (C3) 10 wt % limestone amendment; (C4) 5 wt % half ordinary Portland cement and half fly ash amendment; and (C5) 5 wt % ordinary Portland cement amendment. The control cell showed an acidic behavior (pH < 4.5) with variable concentrations of Fe, Al, Zn, and Cu. The amendments were used to neutralize the acidic leachates and decrease dissolved metal concentrations. Leachates from surface runoff samples of amended cells were less loaded with metals compared to samples of vertical infiltration. All amendment formulations increased the pH of the leachates from approximately 4 to circumneutral values. Furthermore, metal and metalloid concentrations were greatly limited, except for Cr and As for the carbonate-based amendments. Metal(-oid) stabilization was successfully achieved using the different amendment formulations, with the exception of C2, which still released As.

The Economic-Environmental Impacts of China’s Action Plan for Soil Pollution Control

To effectively control soil pollution, an action plan (called Soil Plan) was carried out by Chinese government in 2016, which may cost CNY 1.14 trillion during the 2016–2020 period. To evaluate the potential impacts of this action plan on the national economy and environmental control, this study employed a closed macro input-output model to quantitatively account for the economic and environmental impacts from the view of the whole domestic supply chain. Our results show that the implementation of the Soil Plan may stimulate economic development and bring more jobs. It will help generate a gross domestic product (GDP) of CNY 2.72 trillion, with CNY 358.11 billion (15%) made from direct contributions, and CNY 2.36 trillion (85%) from indirect contributions. Meanwhile, the scheme could also produce 2 million jobs within five years, of which 580,000 (29%) are a direct contribution, and 1.42 million (71%) are an indirect contribution. On the other hands, increased demands for products and services of various sectors (such as power/heat production and supply, and chemical products) would also cause more air and water pollutants along with domestic supply chains. The emissions of sulfur dioxide(SO2), nitrogen oxide(NOx), chemical oxygen demand (COD) and ammonia nitrogen(NH3-N) would increase by a total of 5.20 × 105 t, 5.27 × 105 t, 1.62 × 105 t and 9.36 × 103 t, respectively. Our results may raise the concern about the indirect impacts of an environmental policy for the policy maker from both economic and environmental perspectives.

Effectiveness of pig sludge as organic amendment of different textural class mine tailings with different periods of amendment-contact time

The present study assesses the effect of tailing texture (loamy sand (LT) and sandy loam (ST)), dose of pig sludge (0, 50, 100 and 200 t ha^-1) and amendment-contact time (14, 28 and 42 days) on physicochemical quality of amended substrate using Lolium perenne var Nui as a bioindicator. The main properties of LT differed of ST in levels of total organic carbon (0.19 and 0.58%), in pH (4.6 and 8.5), total Cu (202 and 1647 mg kg^-1) and Zn content (31 and 137 mg kg^-1). Soil pore water of experimental substrates was characterized for pH, electrical conductivity (EC) and Cu²⁺ ion activity (pCu²⁺) while ammonium nitrogen (NH₄⁺-N), infiltration rate and general physicochemical characteristics were measured in substrates. Shoot biomass (SB), root biomass (RB) and the RB:SB ratio was calculated for L. perenne. The results showed there to be a significant interaction (p < 0.05) between tailing texture, sludge dose and amendment-contact time for pCu²⁺, infiltration rate, SB, RB, and RB: SB ratio, but not for pH, EC, or NH₄⁺-N. However, sludge dose and amendment-contact time significantly affected all variables. By increasing dosages of pig sludge, pore water pH increased, and this was associated with decreases in pCu²⁺ and the infiltration rate. High doses of pig sludge (100 and 200 t ha^-1) impaired growth of L. perenne irrespective of tailing texture and amendment-contact time, likely because of the rise of EC (up to 14 mS cm^-1). For both tailing textures, the highest biomass was obtained after incorporation of 50 t ha^-1 of pig sludge, with increasing values as amendment-contact time rose. In conclusion, effective management of pig sludge for tailing reclamation should guarantee doses <50 t ha^-1 and amendment-contact time >28 days, irrespective of tailing texture.

Amending potential of organic and industrial by-products applied to heavy metal-rich mining soils

Mining activities promote the development of economies and societies, yet they cause environmental impacts that must be minimized so that their benefits overcome the likely risks. This study evaluated eco-friendly technologies based on the use of low-carbon footprint wastes and industrial by-products as soil amendments for the revegetation of Zn-mining areas. Our goal was to select adequate soil amendments that can be used to recover these areas, with a focus on low-cost materials. The amendments - limestone, sewage sludge, biochar, and composted food remains - were first characterized concerning their chemical composition and structural morphologies. Soil samples (Entisol, Oxisol, Technosol) from three different areas located inside an open-pit mine were later incubated for 60 days with increasing doses of each soil amendment, followed by cultivation with Andropogon gayanus, a native species. The amendments were able to change not only soil pH, but also the phytoavailable levels of Cd, Zn, and Pb. Limestone and biochar were the amendments that caused the highest pH values, reducing the phytoavailability of the metals. All amendments improved seed germination; however, the composted food remains presented low levels of germination, which could make the amendments unfeasible for revegetation efforts. Our findings showed that biochar, which is a by-product of the mining company, is the most suitable amendment to enhance revegetation efforts in the Zn-mining areas, not only because of its efficiency and cost, but also due to its low carbon footprint, which is currently the trend for any "green remediation" proposal.

Contamination of heavy metals and isotopic tracing of Pb in surface and profile soils in a polluted farmland from a typical karst area in southern China

Farmland top soils and soil profiles situated in the karst area of Guilin, Guangxi Zhuang Autonomous Region, southern China, reveal different degrees of heavy metal pollution, both in respect to the lateral as well as the vertical dimension. Pb isotope ratios clearly identify that heavy metal contributions to the soil represent the legacy of former Pb-Zn mining and smelting in the area. Depending upon soil properties, differences in the intensity of the vertical penetration of heavy metal pollution are discernible. Top soil coverage by local farmers provides little remediation. Consequently, hazardous conditions for the regional ecology, for agricultural usage and ultimately for human health remain in place. Based on chemical and isotopic results obtained, more effective remediation strategies need to be developed.