Using cemented paste backfill to tackle the phosphogypsum stockpile in China:A down-to-earth technology with new vitalities in pollutant retention and CO_(2) abatement

Phosphogypsum(PG),a hard-to-dissipate by-product of the phosphorus fertilizer production industry,places strain on the biogeochemical cycles and ecosystem functions of storage sites.This pervasive problem is already widespread worldwide and requires careful stewardship.In this study,we review the presence of potentially toxic elements(PTEs)in PG and describe their associations with soil properties,anthropogenic activities,and surrounding organisms.Then,we review different ex-/in-situ solutions for promoting the sustainable management of PG,with an emphasis on in-situ cemented paste backfill,which offers a cost-effective and highly scalable opportunity to advance the value-added recovery of PG.However,concerns related to the PTEs'retention capacity and long-term effectiveness limit the implementation of this strategy.Furthermore,given that the large-scale demand for ordinary Portland cement from this conventional option has resulted in significant CO_(2) emissions,the technology has recently undergone additional scrutiny to meet the climate mitigation ambition of the Paris Agreement and China's Carbon Neutrality Economy.Therefore,we discuss the ways by which we can integrate innovative strategies,including supplementary cementitious materials,alternative binder solutions,CO_(2) mineralization,CO_(2) curing,and optimization of the supply chain for the profitability and sustainability of PG remediation.However,to maximize the co-benefits in environmental,social,and economic,future research must bridge the gap between the feasibility of expanding these advanced pathways and the multidisciplinary needs.

Erosion wear at the bend of pipe during tailings slurry transportation:Numerical study considering inlet velocity,particle size and bend angle

Pipeline hydraulic transport is a highly efficient and low energy-consumption method for transporting solids and is commonly used for tailing slurry transport in the mining industry.Erosion wear(EW)remains the main cause of failure in tailings slurry pipeline systems,particularly at bends.EW is a complex phenomenon influenced by numerous factors,but research in this area has been limited.This study performs numerical simulations of slurry transport at the bend by combining computational fluid dynamics and fluid particle tracking using a wear model.Based on the validation of the feasibility of the model,this work focuses on the effects of coupled inlet velocity(IV)ranging from 1.5 to 3.0 m·s^(-1),particle size(PS)ranging from 50 to 650μm,and bend angle(BA)ranging from 45°to 90°on EW at the bend in terms of particle kinetic energy and incidence angle.The results show that the maximum EW rate of the slurry at the bend increases exponentially with IV and PS and first increases and then decreases with the increase in BA with the inflection point at 60°within these parameter ranges.Further comprehensive analysis reveals that the sensitivity level of the three factors to the maximum EW rate is PS>IV>BA,and when IV is 3.0 m/s,PS is 650μm,and BA is 60°,the bend EW is the most severe,and the maximum EW rate is 5.68×10^(-6)kg·m^(-2)·s^(-1).In addition,When PS is below or equal to 450μm,the maximum EW position is mainly at the outlet of the bend.When PS is greater than 450μm,the maximum EW position shifts toward the center of the bend with the increase in BA.Therefore,EW at the bend can be reduced in practice by reducing IV as much as possible and using small particles.

Hydration reactivity difference between dicalcium silicate and tricalcium silicate revealed from structural and Bader charge analysis

Cement hydration is the underlying mechanism for the strength development in cement-based materials.The structural and electronic properties of calcium silicates should be elucidated to reveal their difference in hydration reactivity.Here,we comprehensively comparedβ-C_(2)S and M_(3)-C_(3)S and investigated their structural properties and Bader charge in the unit cell,during surface reconstruction and after single water adsorption via density functional theory.We identified different types of atoms inβ-C_(2)S and M_(3)-C_(3)S by considering the bonding characteristics and Bader charge.We then divided the atoms into the following groups:forβ-C_(2)S,Ca and O atoms divided into two and four groups,respectively;for M_(3)-C_(3)S,Ca,O,and Si atoms divided into four,four,and three groups,respectively.Results revealed that the valence electron distribution on the surface was more uniform than that on the unit cell,indicating that some atoms became more reactive after surface relaxation.During water adsorption,the electrons ofβ-C_(2)S and M_(3)-C_(3)S were transferred from the surface to the adsorbed water molecules through position redistribution and bond formation/breaking.On this basis,we explained whyβ-C_(2)S and M_(3)-C_(3)S had activity differences.A type of O atom with special bond characteristics(no O–Si bonds)and high reactivity existed in the unit cell of M_(3)-C_(3)S.Bader charge analysis showed that the reactivity of Ca and O atoms was generally higher in M_(3)-C_(3)S than inβ-C_(2)S.Ca/O atoms had average valence electron numbers of6.437/7.550 inβ-C_(2)S and 6.481/7.537 in M_(3)-C_(3)S.Moreover,the number of electrons gained by water molecules in M_(3)-C_(3)S at the surface was higher than that inβ-C_(2)S.The average variations in the valence electrons of H_(2)O onβ-C_(2)S and M_(3)-C_(3)S were 0.041 and 0.226,respectively.This study further explains the differences in the hydration reactivity of calcium silicates and would be also useful for the design of highly reactive and environmentally friendly cements.

Editorial for special issue on frontiers and advances in cemented paste backfill

As an important guarantee for human survival and development,the increasing use of mineral resources has led to the generation of a large amount of tailings and slags.However,with the deep promotion of green concepts such as solid waste resource utilization and sustainable development,adding additives to tailings as filling materials can not only improve resource utilization efficiency and prevent surface collapse,but also reduce solid waste discharge to the surface,which is an effective way to fully utilize tailings resources and achieve land and energy saving,environmental protection,and waste utilization.

Guidance and review:Advancing mining technology for enhanced production and supply of strategic minerals in China

Mineral resources,often referred to as“industrial food,”play a pivotal role in the national economic construction sector.Specifically,strategic minerals(SMs)bear a direct influence on the development of emerging strategic industries within China.This paper aims to shed light on the supply and demand dynamics,current status,and characteristics of SMs from the perspective of China's national security.We offer a comprehensive review of the current status and challenges associated with SM mining technology in China.Our analysis spans various mining methods,including open-pit mining,deep underground mining,green mining of complex underground bodies,integrated underground mining and processing,and intelligent mining.Within this framework,we delve into multiple initiatives aimed at improving the status of the mining industry,increasing production,and maintaining the adequate supply of these resources.We discuss these strategies from both a top-level policy and system design perspective,as well as detailed implementation plans.

Enhancing CO_(2)mitigation potential and mechanical properties of shotcrete in underground mining utilizing microbially induced calcium carbonate precipitation

Achieving low-carbon development in the mining sector is fundamental for global carbon emissions abatement,especially considering the growing demand for mineral resources.Currently,the energy foot-print of mines emerges as the main carbon contributor.While cleaner energy sources have the potential for reducing emissions,transitioning to these sources remains challenging.This study presents a practical CO_(2)mitigation strategy for underground mining by integrating bacteria into shotcrete to enhance exca-vation.The findings demonstrate that bacteria can capture CO_(2)from the atmosphere,thereby increasing the carbonation reactions.X-ray diffraction(XRD),scanning electron microscope(SEM)and energy dis-persive spectrometer(EDS)analysis shows the captured CO_(2)present in the forms of calcite,vaterite,and aragonite.The formed carbonates intermingled with the precipitated calcium-silicate-hydrate(C-S-H)at relatively low bacteria additions,densifying the cementitious matrix and improving the mechan-ical properties.However,high bacteria concentrations lead to excess carbonates that consume C-S-H pre-cipitation,counteracting the benefits of carbonation and reducing mechanical strength.Optimal results were achieved with 0.3%bacteria by mass fraction,potentially mitigating 0.34 kg/m^(2)of CO_(2),which is approximately equivalent 567 g of CO_(2)absorbed by 1 g of bacteria based on the effectiveness demon-strated in this study.These findings are crucial for advancing emissions control in mining and supporting climate goals outlined in the Paris Agreement.

Identifying mining-induced chromium contamination in soil through visible-near infrared spectroscopy and machine learning

The extraction,purification,and utilization of mineral resources have been among the largest anthropogenic sources of chromium(Cr)in soil.Determining Cr contamination in soil is a key issue prior to its appropriate remediation.Nevertheless,the efficient identification of large-scale soil Cr contamination requires continuous research.The present study proposes a continental-scale method to rapidly identify soil Cr contamination using visible-near infrared spectroscopy(vis-NIR)and machine learning(ML).A large dataset containing 18,675topsoil samples from the Land Use/Land Cover Area Frame Survey 2009 projects across Europe was compiled.Five advanced ML algorithms were compared,and hyperparameter optimization was conducted using the grid search method.Permutation importance was employed to calculate the rank of each spectral wavelength,shedding light on the most sensitive spectral wavelength for Cr contamination.Results indicate that hyperparameter optimization had the most significant performance improvement on support vector machine(SVM),exhibiting an increase in training performance from 0.795 to 0.868.The achieved optimal SVM accuracy,area under the receiver operating feature curve,sensitivity,and specificity of 0.78,0.85,0.85,and 0.66,respectively,indicating excellent predictive performance on the Cr contamination classification.The optimal SVM model revealed that the most important spectral band for classifying Cr contamination was 1430-1433 nm.This finding implies that the adsorption of molecular water was closely related to the classification of Cr contamination.The current study introduces the first continental-scale identification of Cr contamination using visNIR,which has excellent guiding significance for Cr remediation and the identification of other heavy metals using vis-NIR.