Enhanced solidification/stabilization (S/S) of fluoride in smelting solid waste-based phosphogypsum cemented paste backfill utilizing biochar: Mechanisms and performance assessment.

Phosphogypsum (PG) cemented paste backfill (CPB) is a primary non-hazardous method for treating PG. However, using traditional binders like cement increases global carbon emissions and mining operational costs while complicating the reduction of fluoride leaching risks. This study introduces a novel PG-based CPB treatment method using steel slag (SS) and ground granulated blast furnace slag (GGBFS) as binders, calcium oxide as an exciter, with biochar serving as a fluoride-fixing agent. We investigated the effect of biochar addition on the hydration and solidification/stabilization (S/S) of fluoride in SS and GGBFS-PG-based materials (SSPC). The results indicated that the optimal strength and performance for fluoride S/S were achieved with a biochar addition of 0.2 wt%. Compared to the control group without biochar, the strength increased by 54.3%, and F leaching decreased by 39.4% after 28 days of curing for SSPC. The addition of 0.2 wt% biochar facilitated heterogeneous nucleation and acted as a microfiller, enhancing SSPC's properties. However, excessive biochar reduced the compactness of SSPC. Additionally, the distribution of fluoride was strongly correlated with P, Ca, Fe, and Al, suggesting that fluoride S/S is linked to the formation of stable hydration products like fluorapatite, fluorite, and complexes such as [AlF6]3- and [FeF6]3-. These findings offer a promising approach for the safe treatment of PG and the beneficial reuse of solid waste from SS and GGBFS.

Geomechanical aspects of stabilizing arsenic trioxide roaster waste in cemented paste backfill at the Giant Mine, Canada.

Giant Mine, an abandoned gold mine near Yellowknife in the Northwest Territories of Canada, generated significant arsenic trioxide roaster waste (ATRW) during its operations, posing a substantial environmental hazard. This study explored the feasibility of stabilizing ATRW by incorporating it into cemented paste backfill (CPB). Using response surface methodology (RSM), CPB samples with varying mixing ratios were analyzed to identify key parameters influencing strength. Unconfined compressive strength (UCS) tests assessed physical stability, while saturated hydraulic conductivity and computed tomography (CT) analyses examined the microstructure of the CPB. The results revealed that CPB samples prepared with general use (GU) cement exhibited significantly higher strength than those with a GU and lime kiln dust (LKD) mixture. Binder and solid contents were identified as the most critical factors influencing UCS, with binder content having a more pronounced influence. Curing time was found to be non-significant. Higher binder and solid contents correlated with higher UCS values in the CPB samples. The addition of 10% wt. ATRW reduced the UCS by over 30%, particularly in samples with lower binder and solid contents. Although microstructure differences were not evident in saturated hydraulic conductivity tests, CT scans showed increased formation of high-density arsenic-containing materials in samples with the highest UCS, especially those using GU binder. These findings suggest that optimizing binder and solid contents is crucial for enhancing CPB strength and effectively stabilizing ATRW.

A method to investigate muscle target-specific transcriptional signatures of single motor neurons.

BACKGROUND: Motor neurons in the vertebrate spinal cord have long served as a paradigm to study the transcriptional logic of cell type specification and differentiation. At limb levels, pool-specific transcriptional signatures first restrict innervation to only one particular muscle in the periphery, and get refined, once muscle connection has been established. Accordingly, to study the transcriptional dynamics and specificity of the system, a method for establishing muscle target-specific motor neuron transcriptomes would be required. RESULTS: To investigate target-specific transcriptional signatures of single motor neurons, here we combine ex-ovo retrograde axonal labeling in mid-gestation chicken embryos with manual isolation of individual fluorescent cells and Smart-seq2 single-cell RNA-sequencing. We validate our method by injecting the dorsal extensor metacarpi radialis and ventral flexor digiti quarti wing muscles and harvesting a total of 50 fluorescently labeled cells, in which we detect up to 12,000 transcribed genes. Additionally, we present visual cues and cDNA metrics predictive of sequencing success. CONCLUSIONS: Our method provides a unique approach to study muscle target-specific motor neuron transcriptomes at a single-cell resolution. We anticipate that our method will provide key insights into the transcriptional logic underlying motor neuron pool specialization and proper neuromuscular circuit assembly and refinement.

Fluorides immobilization through calcium aluminate cement-based backfill: Accessing the detailed leaching characterization under torrential rainfall.

Urbanization and economic development have increased the demand for fertilizers to sustain food crop yields. Huge amounts of by-products, especially phosphogypsum (PG), are generated during the wet processing of rock phosphate to produce fertilizers. Chronic exposure to fluoride in phosphogypsum in groundwater as a result of the weathering of fluoride-containing waste poses a significant health risk to millions of people. We propose a method for using calcium aluminate cement (CAC) to remediate high fluoride contents in solid waste. Column leaching tests under harsh rainfall conditions confirmed the efficient fluoride immobilization capacity of a CAC binder. Although the fluoride concentrations in leachates during the first 1-2 days (1.25 mg/L) slightly exceeded the threshold of 1.00 mg/L, the concentrations over 3-28 days (ranging from 0.98 to 0.83 mg/L) consistently remained well within the acceptable range. Furthermore, our characterization and geochemical modeling revealed the fluoride retention mechanisms of CAC-stabilized PG under laboratory-simulated conditions of torrential rainfall. During leaching, physical encapsulation prevents fluoride from contacting leachate. However, an unfavorable pH value can cause the release of fluoride from the cement matrix, which is subsequently captured by aluminate hydrate through adsorption or co-precipitation. We quantified the carbon footprint of CAC for immobilizing 1 mg of fluoride in PG, obtaining a remarkably low value of 4.4 kg of CO2, in contrast to the emissions associated with the use of ordinary Portland cement (OPC). The findings suggest a unique opportunity for extensive PG remediation. This opportunity extends the horizons of achieving zero-waste emissions in the phosphorus industry and has practical significance in the context of reducing carbon emissions.

Basic characteristics of magnesium-coal slag solid waste backfill material: Part I. preliminary study on flow, mechanics, hydration and leaching characteristics.

The environmental damage caused by surface subsidence and coal-based solid waste (CBSW) is a common problem in the process of coal mining. Backfill mining can control the mining-induced subsidence and solve the problem of bulk solid waste storage. In the present work, a magnesium-coal slag solid waste backfill material (MCB) with modified magnesium slag (MS) as binder and CBSW (fly ash (FA), flue gas desulfurization gypsum (FDG) and coal gasification slag (CGS)) as supplementary cementitious material/aggregate was proposed to meet the needs of coal mining in Northern Shaanxi, China, to realize the comprehensive treatment of goaf and CBSW. The results show that: (1) The rheological curve of the fresh MCB slurry is highly consistent with the Herschel-Bulkley (H-B) model, and its fluidity meets the basic requirements of mine backfill pumping. With the addition of FDG and MS, the yield stress, apparent viscosity and thixotropy of MCB slurry increase, while the pseudoplastic index and slump decrease. (2) The strength of MCB develops slowly in the early stage (0∼14 days) and increases rapidly in the later stage (14∼90 days). Except for the ratio of M20F1 and FDG = 0%, the strength of samples at other ratios (at 28 days) is between 6.06∼11.68 MPa, which meets the strength requirement of 6 MPa for coal mine backfill. The addition of MS and appropriate amount of FDG is beneficial to the development of strength. In contrast, MS exhibits a significant improvement in early strength, and FDG has a significant improvement in late-age strength. (3) Corresponding to the compressive strength, the hydration products C-S(A)-H and AFt of MCB are less in the early stage and greatly increased in the later stage. The active substance in FA/CGS will undergo pozzolanic reaction with the MS hydration product CH. The addition of FDG and MS can promote the reaction and increase the amount of hydration product, but in contrast, the promotion effect of FDG is more significant. (4) The amount of heavy metal leaching of MCB meets the requirements of national standards. The hardened MCB has a solidification/stabilization effect on heavy metal elements, which can significantly reduce the amount of heavy metal leaching. The results imply that MCB is a safe, reliable, and eco-friendly solid waste backfill material, and its application is conducive to the coordinated development of coal resource mining and environmental protection.

Sustainable controlled low strength material from waste materials for infrastructure applications: State-of-the-art.

In recent years, controlled low strength material (CLSM) has been utilized as an alternate backfill material for various infrastructure applications such as filling of voids, construction of pavement bases, trench backfilling, bed for pipelines, etc. Efforts have been made by researchers to utilize various waste materials/industrial by-products such as slag, fly ash, pond ash, cement kiln dust, red mud, sludge, construction and demolition waste and crumb rubber for development of sustainable CLSM. The present work discusses in details the evolution of CLSM, recent advances in the development of CLSM with different waste materials/industrial by-products, and the effect of these sustainable materials on flowability, strength, hardening time and other properties of CLSM. Further, the benefits/challenges and applications of different sustainable CLSM mixes have been compared. The inferences from pilot/field scale studies for CLSM and alkali activated CLSM have been discussed, and assessment of the sustainability coefficient of select CLSM combinations considered from the literature have been performed. The study quantifies the sustainability of different CLSM mixes, and presents the challenges that needs to be addressed in future to increase the utilization of sustainable CLSM for future infrastructure development.

Microstructure and mechanical behavior of cemented gold/tungsten mine tailings-crushed rock backfill: Effects of rock gradation and content.

Without appropriate and responsible waste management in place, the cursory storage of tailings and waste rocks on the surface can cause devastating damage to the planet's ecosystems. To proactively manage or abolish the damage, some techniques such as mine backfill have been already used repeatedly in mines. Microstructure and strength behavior of cementitious tailings-crushed rock backfill (CTCRB) with gold/tungsten tailings and rock contents (e.g., 10%, 20%, 30%, 40%, and 50%) were conducted in this study by using both UCS (unconfined compressive strength) tests (e.g., peak strengths, stress-strain curves, failure modes) and SEM micro-graphs. Key conclusions were shown that: when gradation and content of crushed rock was considered as 1-3 mm and 50% respectively, the UCS value of gold tailings based backfills was 1.02 MPa. In contrast, the UCS value of tungsten mine tailings based backfills was 1.36 MPa when the amount of crushed rock within the filling matrix became 10%. Tungsten tailings based backfills were more sensitive to crushed rock gradation than gold tailings based backfills. CTCRB's stress-strain curvatures were up-concave in the step of pore compaction. With the increase in the content and gradation of crushed rock, tungsten tailings based backfills showed swelling and crushing in complete destruction. Tailings' particle size, crushed rock content and gradation utterly affected the failure modes of CTCRB. Ettringite/CSH gel was found to be the leading hydration materials in the backfill matrix. The micro-cracks within CTCRB specimens were unfavorably correlated with its UCS data. To conclude, this study's main outcomes could give a significant guide for CTCRB's industrial uses.

Comparative study of radon sources and associated health risk in four underground uranium mines.

This paper presents a comparative study of the quantitative estimation of 222Rn and its health risk from various sources in four underground uranium mines. 222Rn exhalation rates from uranium-bearing rocks and backfill materials were estimated by calculating the 222Rn concentration accumulated in an enclosed chamber into which radon was exhaled. This comparative study indicates a more significant effect of porosity on the exhalation rates. Dissolved 222Rn in mine water was estimated using scintillation cell and bubbler kit. The discrepancy in 222Rn concentration in the mines might be attributed to the variation in geological features, ore grade, and porosity. This study revealed that the maximum radon exposure was produced from the backfill mill tailings, followed by uranium ore and mine water in the mines. The radon dose values in the individual mines remained under the safe dose limit of 20 mSv year-1. The excess lifetime cancer risk (ELCR) and 222Rn-induced lung cancer cases (RnLCC) per million persons per year were also estimated.

PET waste management in Pakistan through use of PET shreds as additive in backfill soil.

The management of waste plastic bottles is one of the major environmental challenges in the world. Plastic bottles are composed of polyethylene terephthalate (PET), which is non-biodegradable, resulting in environmental problems. Various studies have been carried out on the use of waste PET bottles in the form of custom-made strips as a stabilizer. However, no significant research has been carried out on the use of waste PET bottle shreds already available in the market. These shreds do not require any special technology or arrangement for bulk production. In this study, the shear strength of low plastic silty clay was improved using locally available PET shreds, and their prospective application in the backfill soil was investigated. Standard Proctor tests and direct shear tests were conducted on soil stabilized with three different sizes of plastic shreds (2 mm, 6 mm, and 10 mm) in four different percentages (1%, 3%, 5%, and 10%). Findings revealed that adding PET shreds in 1% content improves the shear strength characteristics. However, the shear strength parameters decrease with further increase in PET shred content. Therefore, PET shreds in 1% content can be added in backfill soil to improve its shear strength. Pakistan needs to construct 0.77 million housing units annually to keep up with its population growth. The statistics of seven major cities of Pakistan show that the PET waste management issue of Pakistan can be resolved by using PET shreds as a backfill additive in only 32% of the new houses required to be constructed.

Retention of phosphorus and fluorine in phosphogypsum for cemented paste backfill: Experimental and numerical simulation studies.

The solidification/stabilization of phosphogypsum using cemented paste backfill (OCPB) provides a low-cost and alternative in-situ technique for recycling phosphogypsum stockpiles. But the OCPB is far from obtaining steady states in which the pollutants would redistribute as a response to dynamic environmental conditions. Further, the associated chemical interactions and the mineralogy information of the solubility-controlling phases of contaminants (fluorine and phosphorus) have not been thoroughly studied or fully understood. In this study, a framework coupling the chemical, mineralogical, and morphological analyses is used to determine the fluoride and phosphate retention mechanisms of immobilized OCPB. Then the pH-dependent leaching tests and numerical simulation is applied as a useful tool to identify the minerals controlling stabilized OCPB leaching behavior. The overall findings proved that aluminate-rich calcium silicate hydrates play an essential role in fluoride and phosphate retention. Both experimental and simulational acid neutralization and leaching curves indicate that the cementitious matrix works as a strong buffering material ensuring high pH conditions that are necessary for fluorine and phosphorus retention. Although discrepancies were observed in absolute fluorine and phosphorus leaching values at highly acidic conditions, the simulations are able to describe highly amphoteric leaching behavior. The simulation suggests that the aluminum species and calcium phosphates governed the solubility of fluorine and phosphorus, respectively. The results of this work would have implications for predicting the leaching behavior of OCPB in detrimental and multiple environments.

Recycling of arsenic-containing biohydrometallurgy waste to produce a binder for cemented paste backfill: Co-treatment with oil shale residue.

The high cost of ordinary Portland cement (OPC) limits the broad usage of cemented paste backfill (CPB). Additionally, improper disposal of arsenic-containing biohydrometallurgy waste (BW) can cause tremendous pollution to the environment. Consequently, BW is used to prepare an alternative cementitious material for CPB in this study. The effect of calcined oil shale residue (COSR) on the binder's characteristics was studied. The reaction kinetics of the binder in the presence of COSR were studied via the isothermal calorimeter test and the Krstulovic-Dabic model; mechanical strength and hydration product modifications due to the addition of COSR were also investigated. The leaching of hazardous elements from the binder was also investigated. The results showed that adding COSR reduced the flowability of fresh slurry and early-age compressive strength; however, adding 20 wt% COSR resulted in the highest later age compressive strength, thereby reaching ∼43.65 MPa after 60 days. The compressive strength of the CPB sample using the COSR20 as a binder may reach ∼87% of the OPC-based CPB sample. Furthermore, the presence of COSR had no significant effect on the phase assembles but changed the amount of ettringite (AFt) and calcium silicate aluminate hydrate (C-A-S-H). The results of this study show that the prepared binder could be used as an alternative to OPC in CPB.

Physico-chemical and micro-structural behavior of cemented mine backfill: Effect of pH in dam tailings.

The tailings created during ore processing have been a serious problem for mining companies and environment since it is a challenging task to effectively manage these highly voluminous/dangerous tailings. Therefore, several tailings disposal methods like tailings dams are needed for sustainable mining operations. The tailings accumulated in the dams reflect a critical raw material source since they might contain key base/precious metals, such as Au, Ag, Co, Ni, Cu and Zn. This study deals with the use-ability of dam tailings in cemented mine/paste backfill (CMB/CPB), considering the physico-chemical and micro-structural aspects. The backfill mixtures were manufactured at 76 wt% solid and 5 wt% cement contents, exposed to cure for up to 56 days, and tested for determining their strength (UCS), geo-chemical (i.e., pH, redox potential, and conductivity) and microstructure (i.e., XRD, TGA, and SEM) characteristics. Results disclosed that the strength of backfill was improved by the augmented basicity/age while only backfills made with sulfide-rich tailings had a noticeable drop in strength. This can be enlightened by the types of tailings (aged and fresh), and the hydration products shaped owing to the interaction of these tailings mixed with cement. While the values of pH detected by chemical tests were amplified up to 14 days, some decreased up to 56 days due to acid formations and erosions. This is the key function of CPB's deterioration physically, chemically, and microstructurally. Lastly, the outcomes of this study will allow us to further explore/assess the effects of dam tailings' potential usages on quality/performance of backfill mixtures.

Experimental study on the triaxial mechanical behaviors of the Cemented Paste Backfill: Effect of curing time, drainage conditions and curing temperature.

The application of CPB (Cemented Paste Backfill) can realize the clean, efficient, and safe mining of underground metal mines. Clear understanding on the triaxial mechanical properties of CPB is important to the CPB design and the stability analysis of the backfilled CPB structure. The triaxial mechanical properties of CPB can be significantly affected by the different curing conditions. In this research, triaxial compression tests of the CPB samples were carried out using the GCTS (Geotechnical Consulting & Testing System), and the considered curing conditions include different curing time (1, 3, 7 and 28 days), drainage conditions (drained and undrained) and curing temperatures (20 °C, 35 °C and 45 °C). The measured mechanical parameters were compared and analyzed against the framework of the Mohr-Coulomb criterion. Then, the vertical stress distribution of the backfilled CPB structure was calculated and discussed using the measured mechanical parameters. The results show that with the increase of the lateral constraint ratio (σc/Sd0), the elastoplastic stage of the measured deviator stress versus axial strain curve of CPB sample is gradually obvious. The peak deviator stress (Sdp) and the ultimate axial strain (εu) show the linear and negative exponential increase with the σc/Sd0 respectively. The number of cracks on the fractured surface of the CPB samples gradually decreased with the increase of σc/Sd0. The failure types of CPB samples were changed from tensile failure (σc/Sd0 = 0%) to the mixed tensile-shear failure (σc/Sd0≈10%) and compression-shear failure (σc/Sd0≥20%). Moreover, with the increase of curing time and curing temperature or under the drained curing condition, the peak deviator stress and cohesion (cb) of CPB can be significantly increased, but the corresponding internal friction angle (ϕb) is decreased. The shear mechanical parameters of CPB can significantly affect the vertical stress distribution inside the CPB structure. Therefore, when estimating the vertical stress distribution inside the backfilled CPB structure in engineering practices, it is necessary to focus on the changes of CPB shear parameters (cb and ϕb) caused by different curing conditions.

Determination of utilization strategies for hemihydrate phosphogypsum in cemented paste backfill: Used as cementitious material or aggregate.

Due to the prominent advantages of low cost and efficient utilization, cemented hemihydrate phosphogypsum (HPG) backfill is becoming popular in mine goaf treatments in China as a new promising branch of cemented paste backfill (CPB). The HPG gelling activity time dependence determines its role in CPB, that is, whether it is used as a cementitious material or aggregate. Laboratory and field experiments showed that the HPG gelling activity decreases with an increasing aging time due to the gradual HPG conversion from the hemihydrate to the dihydrate form. The HPG conversion can be described by the Avrami equation, and further divided into acceleratory and slow reaction periods. Soluble P2O5 formed insoluble brushite coatings, significantly inhibiting the HPG conversion. Increasing the Al2O3 content and reducing temperature further retarded the HPG conversion. Reducing the temperature inside the stacks by lowering their stacking height delayed the HPG gelling activity decay. At a stacking height of 1.5 m, HPG can be prepared into cementitious materials for common CPB methods within the first 137 h of aging, thereafter it can only be used as an inactive aggregate. Finally, an application case is presented to illustrate the effectiveness of the utilization strategies in guiding the use of HPG in CPB.

Impact of Retained Cystoscopy Fluid after Laparoscopic Hysterectomy: A Randomized Controlled Trial.

STUDY OBJECTIVE: To investigate the impact of retained cystoscopy fluid after laparoscopic hysterectomy on time to spontaneous void, time to discharge, urinary retention, bladder discomfort, and patient satisfaction. DESIGN: Single-blind randomized controlled trial. SETTING: An academic medical center. PATIENTS: One hundred and twenty patients who underwent laparoscopic hysterectomy with universal cystoscopy for benign indications, excluding pelvic organ prolapse and urinary incontinence indications. INTERVENTIONS: From October 10, 2018, to October 17, 2019, we compared 200 mL retained cystoscopy fluid and complete bladder emptying after laparoscopic hysterectomy with universal cystoscopy. MEASUREMENTS AND MAIN RESULTS: A total of 120 patients were enrolled and randomized (59 in the retained cystoscopy fluid group and 61 in the emptied fluid group). The primary outcome was time to first spontaneous void. The secondary outcomes were time to discharge, urinary retention rates, bladder discomfort, and patient satisfaction. A sample size of 120 was calculated to detect a 57-minute difference in time to spontaneous void. There were minimal differences in baseline demographics and surgical characteristics between the groups. There was an apparent, although not significant, difference in time to void of 25 minutes (143 minutes vs 168 minutes, p = .20). Time to discharge and urinary retention rates did not differ (199 minutes vs 214 minutes, p = .40, and 13.6% vs 8.2%, p = .51, respectively). There was no difference in postoperative bladder discomfort and patient satisfaction. CONCLUSION: Retained cystoscopy fluid after laparoscopic hysterectomy did not significantly affect time to first spontaneous void, time to discharge, urinary retention, bladder discomfort, or patient satisfaction.

Strength Development Monitoring of Cemented Paste Backfill Using Guided Waves.

The strength of cemented paste backfill (CPB) directly affects mining safety and progress. At present, in-situ backfill strength is obtained by conducting uniaxial compression tests on backfill core samples. At the same time, it is time-consuming, and the integrity of samples cannot be guaranteed. Therefore guided wave technique as a nondestructive inspection method is proposed for the strength development monitoring of cemented paste backfill. In this paper, the acoustic parameters of guided wave propagation in the different cement-tailings ratios (1:4, 1:8) and different curing times (within 42 d) of CPBs were measured. Combined with the uniaxial compression strength of CPB, relationships between CPB strength and the guided wave acoustic parameters were established. Results indicate that with the increase of backfill curing time, the guided wave velocity decreases sharply at first; on the contrary, attenuation of guided waves increases dramatically. Finally, both velocity and attenuation tend to be stable. When the CPB strength increases with curing time, guided wave velocity shows an exponentially decreasing trend, while the guided wave attenuation shows an exponentially increasing trend with the increase of the CPB strength. Based on the relationship curves between CPB strength and guided wave velocity and attenuation, the guided wave technique in monitoring the strength development of CPB proves feasible.

A review of additives used in the cemented paste tailings: Environmental aspects and application.

A large amount of mine wastes is generated every year through mining and mineral processing operation. The management of mine tailings is an attractive topic for researchers from both environmental and economic aspects. Mine tailings have shown a capacity as a raw material for the construction industry or a substitution for previous materials to produce the cement. It is applied in some specific environments such as offshores or massive projects like large bridges and tunnels. However, the cement industry has caused a variety of environmental issues. The production of Portland cement on an industrial scale increases the greenhouse effects and generates acidic rains. It releases greenhouse gases by the generation of carbon dioxide. In recent years, strict environmental regulations led to more efforts from mining industries to manage their tailings. A new approach to decrease the environmental issues, improve cement technology and obtain economic benefits is the use of mine tailings for cement production. Mine tailings in the cement mixtures decrease the initial hydration, retard the setting time, and lower the product mechanical strength. These problems can be fixed by the use of additives. Additives as chemical compounds are added to a cemented paste to change its properties and improve its performance. Therefore, the additives in cemented paste tailings can increase the pump-ability, reduce the water-to-cement ratio, increase density, or even adjust setting time and hydration according to the desired purposes. However, the amount of additives in the cemented paste tailings changes based on the type of additive. It should be optimized to cause a positive effect on the cement properties. Furthermore, the additives and their adaptation to the physical and chemical characteristics in cement and tailings is an important issue that should be investigated. In this paper, the usage of several chemical additives was studied, which can strengthen the properties of cemented paste tailings during backfilling operation. It can cause a better condition to decrease the environmental problems for the cement industry and mine tailings. A review of previous works is presented with an explanation of the gaps in previous studies.

Utilization of modified copper slag activated by Na2SO4 and CaO for unclassified lead/zinc mine tailings based cemented paste backfill.

Serious heavy metals pollution was characterized in the lead/zinc mine tailings dam and surrounding soils, as well as copper slag disposal sites. This study investigates the efficacy of modified granulated copper slag (MGCS) as a partial replacement of ordinary Portland cement (OPC) for lead/zinc mine tailings-based cemented paste backfill (CPB) application using Na2SO4 (CSN) and CaO (CSC) as alkali-activated materials. The effect of different scenarios was ascertained by unconfined compressive strength (UCS). Also, the correlated microstructural evolution and mineralogical phase generation were obtained by scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), and X-ray diffraction (XRD). The main findings proved that CSN was more effective in improving mechanical performance. Na2SO4 was found associated with C-S-H gel formation accompanied by a compact microstructure and better pore distribution with lower porosity. However, deposition of chloride compound was found in the surface layer of CSN samples, which could bring deterioration to the mechanical properties. Results above extend the knowledge of reusing MGCS as supplementary material to CPB, promoting the concept of a circular economy demand for both lead/zinc mine extraction and copper industries.

Low carbon binder modified by calcined quarry dust for cemented paste backfill and the associated environmental assessments.

Cemented paste backfill (CPB) favors the sustainable development of mine industry. However, as the primary cementitious binders in CPB, the high cost of ordinary Portland cement (OPC) discourages CPB utilization. In the present work, low-carbon and low-cost binders activated by Na2CO3 supplemented by calcined quarry dust were used in CPB. The binder was prepared using a 'one-part' method. It was found that binders prepared using 8% Na2CO3 and 5% CQD show the best performance. The superior properties of the binders were attributed to the promoted binder hydration and special phase assembles of the hydration products. Cost and carbon emission analysis showed that Na2CO3 activated binder was cheaper and greener. The cost and CO2 emission of binder B8Q5 were lower than OPC by around 34.16% and 87.76%, respectively. Besides, leaching tests showed that all the toxic metals were stabilized, which posed no environmental risk.

Optimal design and setting of rotary strip-tiller blades to intensify dry season cropping in Asian wet clay soil conditions.

Fine-textured clayey soils dominate Asian rice fields that are kept either fallow or cultivated with non-rice crops after harvest of monsoon rice. Use of seeding machinery compatible with the principles of conservation agriculture on such soils, however, has not been promising. Under these conditions - which predominate the population and poverty dense areas of coastal South Asia - such machinery fails to open a furrow or throws excessive soil out of the tilled furrow during strip-till seeding. This results in a poor seed coverage at planting jeopardizing crop establishment. In response, this soil bin study investigated strip-tillage blade designs and settings to optimize rotary strip-till system for wet clay soil conditions common in South Asian rice fields. Three designs of C type rotary blade (conventional, medium and straight) and two blade settings (four and six blades per row; 50 and 100 mm cutting widths) were tested at three blade operating depths (50, 75, and 100 mm) using a tillage test rig and a soil bin, and a high-speed camera to understand the processes of soil cutting, throwing, backfilling, and creation of furrow seedbed. The soil bin soil consisted of a wet sandy-clay-loam soil with a moisture content of 28.2% (85% of field capacity) and was compacted to the bulk density of 1440 kg m-3. Using the test rig, rotary speed of the blades was maintained at 480 rpm and forward speed at 0.4 m s-1. At four blades per row setting, all blades created high amounts of optimum clods (1-20 mm size). The conventional and medium blades threw too much soil out of the strip-tilled furrow while the straight blade created adequate backfill at 75 and 100 mm operating depths. At 6 blades per row setting, all blades produced high amounts of backfill at any depths, but the straight blade also produced the highest amounts of optimum clods and a uniform furrow. Considering machine and energy costs, blade performance, and the necessity of minimizing soil disturbance in strip-tillage, our study indicates that the use of straight blades (four blades per row) operated at a depth of 75 or 100 mm are more ideal. These specifications are likely to enhance strip-tillage stand establishment in fine-textured soils with high moisture contents, though further work is needed under actual field conditions to confirm suitability of the proposed strip-till system for crop establishment in currently fallowed as well as the intensively cropped lands of Asia.