Mine tailings as a raw material in alkali activation: A review

The mining industry produces billions of tons of mine tailings annually.However,because of their lack of economic value,most of the tailings are discarded near the mining sites,typically under water.The primary environmental concerns of mine tailings are related to their heavy metal and sulfidic mineral content.Oxidation of sulfidic minerals can produce acid mine drainage that leaches heavy metals into the surrounding water.The management of tailing dams requires expensive construction and careful control,and there is the need for stable,sustainable,and economically viable management technologies.Alkali activation as a solidification/stabilization technology offers an attractive way to deal with mine tailings.Alkali activated materials are hardened,concrete-like structures that can be formed from raw materials that are rich in aluminum and silicon,which fortunately,are the main elements in mining residues.Furthermore,alkali activation can immobilize harmful heavy metals within the structure.This review describes the research on alkali activated mine tailings.The reactivity and chemistry of different minerals are discussed.Since many mine tailings are poorly reactive under alkaline conditions,different pretreatment methods and their effects on the mineralogy are reviewed.Possible applications for these materials are also discussed.

The potential of arbuscular mycorrhizal fungi to conserve Kalappia celebica,an endangered endemic legume on gold mine tailings in Sulawesi,Indonesia

Kalapi(Kalappia celebica)is an endemic legume of Sulawesi and has been included in the endangered category since the early 1980s.Conservation of the species is possible through ex situ culture techniques.Arbuscular mycorrhizal fungi(AMF)can accelerate plant growth which in turn supports the conservation of endangered species.This study aimed to assess the efficacy of local AMF to accelerate the growth of kalapi and increase nutrient uptake in kalapi grown in gold mine tailing media.There were three AMF treatments,Glomus claroideum,Glomus coronatum,and a mixture of both,plus the control.Each treatment was replicated three times,each consisting of five plants.The results show that the highest AMF colony was obtained by kalapi seedlings inoculated with Glomus coronatum and the mixture of AMF.The range of mycorrhizae inoculation effect values was 59.7–71.3%.AMF inoculation increased growth and dry weight of 4-month-old seedlings compared to controls.Dry and total weights of kalapi inoculated with G.coronatum were significantly different from those inoculated with the AMF mixture.However,they are not significantly different from kalapi inoculated with G.claroideum.The results also show that AMF increased nitrogen and phosphorous uptake by the roots,as well as nitrogen,phosphorous,potassium,manganese and iron by the shoots.All AMF treatments decreased potassium uptake in the roots,except in kalapi inoculated with G.coronatum.The AMF mixture decreased iron contents the roots by 15%.AMF can be developed into biofertilizer to support the conservation of kalapi in tropical Indonesia.

The Micro-Scale Mechanism of Metal Mine Tailings Thickening Concentration Improved by Shearing in Gravity Thickener

Higher concentration is beneficial for the Paste and Thickened Tailings(PTT)operation in metal mine.Partial paste thickeners are produced lower density underflow.Flocculated tailings are intended to form a water entrapped network structure in thickener,which is detrimental to underflow concentration.In this study,the continuous thickening experiment was carried out for ultra-fine tungsten tailings to study the influence of rake shearing on underflow.The micro pores structure and seepage flow in tailings bed before and after shearing are studied by CT and simulation approach to reveal the shearing enhancement mechanism of thickening process.The results shown that,the underflow concentration is increased from 61.4 wt%to 69.6 wt%by rake shearing in a pilot scale thickener,the porosity decreased from 46.48%to 37.46%.The entrapped water discharged from sticks structure more than sphere spaces.In items of seepage,after shearing,the seepage flow channel of tailings underflow is becoming longer,which caused the decreasing average flow rate decreases and absolute permeability.The absolute permeability is negatively correlated with tortuosity.The rake shearing can destroy the flocs structure;change the effective stress to increase the concentration.Higher underflow concentration improves the waste recycling and water recovery rate,especially for arid areas.

Preparation and characterization of CaO-MgO-SiO2 ceramics from silver mine tailings

Silver mine tailings are generated during the exploitation and extraction of silver. Immense amounts of silver mine tailings accumulated in the tailing ponds or backfilled in the mine have resulted in serious dust pollution and heavy metal pollution etc. In this study, ceramics were prepared by using the measure of one step sintering with the mixtures of silver mine tailings, talc and wollastonite, and the impact of silver mine tailings and wollastonite contents on the structure and properties of ceramics were investigated. Moreover, the phase, structure and morphology of ceramics were characterized by methods of XRD, FTIR and SEM. In addition, the apparent porosity, water absorption, volume density, flexural strength and coefficient of thermal expansion of ceramics were tested. The experimental results showed that the optimum performances of ceramics occurred when sintered at 1 200℃ and with raw material consisting of 50 wt% of silver mine tailings, 20 wt% of wollastonite and 30 wt% of talc. The ceramics exhibited excellent properties, with flexural strength of 77.78±8.78 MPa, apparent porosity of(0.4±0.06)%, water absorption of(0.21±0.05)% and a bulk density of 1.93±0.02 g/cm^3. A simple, efficient and economical preparation method of ceramics is presented in this article, which is an effective approach to value-added utilization of silver mine tailings.

Bioremediation techniques for the treatment of mine tailings:A review

Mine tailings(MTs)are the materials dumped on a mining site after mineral extraction,containing scattered traces of residual minerals,dug-up soils,and a disturbed ecosystem.Abandoned and untreated MT can pose threats to the surrounding ecosystem due to the presence of various primary and secondary toxic components,such as organic substances[PAH(polycyclic aromatic hydrocarbons),phenolics]and inorganic materials(sulfur,cyanide),metals and metalloids.All these pollutants originate from nature,and there is a possibility to remedy the problems generated from them.Conventional physical-chemical and biological techniques are often considered for treating the polluted environment and are recognized as having great efficiency.Physicochemical processes,such as incineration,and soil washing with solvents,encounter limitations of cost-effectiveness associated with further environmental concerns.The advantages accompanying bioremediation,the alternative to physicochemical treatment,are its cost-effectiveness,its environmentally benign nature,and complete mineralization of pollutants,instead of the generation of secondary toxic intermediates as in the case of the physicochemical process,make it more attractive for dealing with MT.This manuscript emphasizes use of basic treatment techniques and bioremediation mechanisms for dealing with pollutants from MT that target the revival of nature by utilizing natural agents,plants(phytoremediation),bacteria,fungi,and algae.

Numerical analysis and geophysical monitoring for stability assessment of the Northwest tailings dam at Westwood Mine

The Westwood Mine aims to reuse the tailings storage facility #1(TSF #1) for solid waste storage, but,downstream of the Northwest dike is considered critical in terms of stability. This paper uses numerical modeling along with geophysical monitoring for assessing the Northwest dike stability during the restoration phase. The impact of waste rock deposition in the upstream TSF #1 is considered. The geophysical monitoring is based on electrical resistivity methods and was used to investigate the internal structure of the dike embankment in different deposition stages. The numerical simulations were performed with SLOPE/W code. The results show a factor of safety well above the minimum recommended value of 1.5. Geophysical monitoring revealed a vertical variation in the electrical resistivity across the dike, which indicates a multilayer structure of the embankment. Without any current in situ data, the geophysical monitoring helped estimating the nature of the materials used and the internal structure of the embankment. These interpretations were validated by geological observation of geotechnical log of the embankment. Based on this study, it is recommended that the water polishing pond be partly filled before waste rock is deposited in TSF #1. In addition, to ensure the stability of the dike, the piezometric head monitoring prior to and during waste rock deposition is recommended.

Innovative and sustainable approach for phytoremediation of mine tailings:a review

A review is designed to innovate a sustainable solution for the treatment of mine tailings using bioremediation and phytore-mediation.It emphasizes on achieving the geochemical stability of tailings through the establishment of microbes or plants.It highlights the gaps in achieving the geochemical stability of tailings.Lack of nutrients and low pH discourage the survival of microorganisms and the growth of plants on tailings.Treatment of tailings with agricultural waste(wheat and mustard stalks)would nourish tailings which promote the growth of microorganism and plants.Application of agricultural waste in remediation process is cost-effective.The role of microorganisms such as cyanobacteria,fungi,and algae are well known for mineralogical transformation.Microorganism converts unavailable fraction of nutrient into available form and important initiative to drive tailings towards natural soil.It would support the growth of plants on tailings to achieve successful phy-toremediation.Biofuel generation from tailings through high lipid and protein producing plants is important for sustainable development.Phytoremediation will reduce the environmental impact caused by mine tailings.For phytoremediation,use of biofuel producing plants,i.e.,Jatropha curcus and Brassica juncea,is recommended.

Potential for Use of Iron Mining Tailings Calcined in a Flash Furnace as Pozzolanic Material

This paper presents a study of the potential use of iron mining tailings as artificial pozzolan (metakaolin) after their submission to thermal treatment via calcination in a flash furnace. The research consists of the characterization of the tailings before and after calcination, chemical, mineralogical, thermogravimetric, and mechanical strength analyses were conducted. The results were compared with those for commonly used pozzolans, metakaolin, and similarities were identified. The study of the morphology of the particles before and after calcination was conducted through analyses of images obtained by scanning electronic microscope. The pozzolanic activity of the fine mining tailings calcined with flash technology was evaluated in uniaxial compression trials, which showed excellent results.

Exposure to Fine Particles by Mine Tailing and Lung Function Effects in a Panel of Schoolchildren,Chanaral,Chile

There is much literature on the effects of fine particulate matter (PM2.5) on respiratory and cardiovascular health. However, few studies have evaluated the impact of PM2.5 on a population living in the vicinity of a massive deposit of mine tailings. A longitudinal panel study was performed to evaluate the association between exposure to PM2.5 and acute effects on lung function in schoolchildren from November 2012 to May 2013. Ambient levels of PM2.5 and its metal composition were measured. Lung function was evaluated using spirometric testing. Associations were quantified using GEE multilevel analysis controlling for confounders by using different lag time periods. The chemical characterization of PM2.5 had high levels of S > Na > Cl > Ca > Si > Fe > Al > Mg > K > Cu > Ti > and Zn, which would be associated with metals present in tailings. We found a negative association between the temporal variation of PM2.5 and changes in lung function specifically on forced vital capacity. Our results suggest that schoolchildren exposed to fine particulate matter from tailings deposited in the bay of Chanaral have their forced vital capacity decreased, which would affect their present and future lung development, increasing the risk of developing chronic respiratory diseases.

Comparative Analysis of Metals in Seafood from Rio Doce Coastal Areas and Regional Fish Markets

On November 5, 2015, the Fundão Dam breached (the “Event”), releasing water, tailings, dam construction material, and debris to downstream watercourses. Over 20 million cubic meters of fine particles from the tailings, as well as scoured soil and sediments, reached the Rio Doce estuary and surrounding marine area 17 days later. Fishing was banned by the Federal Court of Espírito Santo in February 2016. The fishing ban area included the coastal area near the mouth of the Rio Doce and seaward to a depth of 25 meters, south to Barra do Riacho, and north to Degredo Beach. In June 2019, the Brazilian health agency, Anvisa, published a risk assessment for fish consumption which recommended daily consumption limits for fish of 200 grams for adults and 50 grams for children for both continental and coastal areas of the Rio Doce basin. Comparative analyses were performed between metal concentrations in marine fish and crustaceans collected in the banned fishing area to reference areas and commercialized seafood markets along the Brazilian coast. The results reveal that metals detected in seafood tissue collected in the fishing ban area are not significantly different than other reference areas or from commercially available seafood. This result indicates that elevated metal concentrations in seafood are a regional problem, unrelated to the Event. Higher concentrations of metals in fish in reference areas outside of the fishing ban area as well as in commercial seafood markets demonstrates that the risk management approach of a localized fishing ban is ineffective for reducing risk to the population related to seafood consumption. .

Enduring legacy of coal mining on the fungal community in a High Arctic soil after five decades

Mineral extraction is known to affect soil fungi in polar environments,but it is unknown how long these effects persist.Here,by amplifying the internal transcribed spacer regions of rRNA genes in soil fungi,we compared soil fungal community in intact natural tundra with that in a nearby former coal mining area,abandoned 52 years previously,on Svalbard in the High Arctic.Compared with those in intact tundra,soils in the former mining area were more acidic and had lower plant coverage.Despite of similar diversity in the two areas,the fungal community was dominated by Basidiomycota in the intact tundra,but by Ascomycota in the former mining area.Ectomycorrhizal genera formed a major part of the tundra community,but were notably less abundant in the mining area.The principal variation among samples was soil pH.Surprisingly,network connectivity analysis indicated that the fungal community in the former mining area had greater network connectivity than that in the tundra area.Overall,the ecosystem in the former mining area has made only limited recovery towards the natural tundra state even after more than five decades.It is unclear whether the recovery of the fungal community is limited more by the low primary productivity,slow migration of fungi and plants,or slow changes in soil parameters.Our findings emphasize the susceptibility of polar ecosystems to disturbance,given their particularly slow recovery back towards the natural state.

Genetic differentiation of Arthrobacter population from heavy metal-contaminated environment

Six samples containing extremely high concen-tration of Pb,Zn,and Cd were obtained from the layers of 5−10 cm and 25−30 cm three tailing piles,with ages of about 10,20 and more than 80 years,respectively.Then,48 bacterial strains were obtained from these samples,and sub-sequently their phylogenetic positions were determined by analysis on the partial sequence of 16S rRNA gene(fragment length ranging from 474 to 708 bp).These isolates were members of the Arthrobacter genus,phylogenetically close to A.keyseri and A.ureafaciens,with sequence ranging from 99.1%to 100%.Furthermore,genetic variation between sub-populations from different samples was revealed by analysis on their randomly amplified polymorphic DNA profile.Nei genetic distance showed that the greatest differentiation occurred between subpopulation A and C.Notably,either genetic distance between subpopulations from the layers of 5−10 cm and 25−30 cm of each tailing pile or between same layers of different tailing pile increased with the history of tailings.Moreover,correlation analysis showed that soluble Pb has a significantly negative relationship with Nei’gene diversity of subpopulation.It was assumed that soluble Pb may be respon-sible for the reduced genetic diversity of the Arthrobacter popu-lation.Our data provided evidence that genetic differentiation of microbial populations was consistent with the changes of environmental factors,particularly heavy metals.