Towards a Sustainable Management of Mine Wastes: Reprocessing, Reuse, Revalorization and Repository

The need for efficient and sustainable management methods of mine waste is continuously growing all around the world. These waste products often present serious management problems due to their more or less significant amounts and possible environmental threats. This Special Issue highlights the recent and new trends in sustainable mine waste management techniques. Currently, it is essential to sustainably manage mine waste, considering social, economic, environmental and technical aspects. In this Special Issue, insights related to the following issues are highlighted: the problems around mine waste, the fine characterization of mine waste, the latest available technical and environmental solutions to efficiently manage mine waste, including treatment and processing before disposal and high value element recovery, with the view of moving towards defining effective, low-cost and ecofriendly methods, the recycling of mine waste products as alternative resources in different sectors, and finally laboratory, pilot and/or industrial-scale studies related to these topics of research. Scientists and industry and governance stakeholders have to face these new challenges to find the best management practices for the future

Phosphate Carbonated Wastes Used as Drains for Acidic Mine Drainage Passive Treatment

This study focused on the removal of heavy metals from a synthetic acid mine water by using continuous column experiments and Phosphate carbonated Wastes as alkaline drains. The passive treatment system targeted aims in neutralizing the acid mine drainage (AMD) containing high concentrations of dissolved iron and other metals. In Morocco, the phosphate mine industry produces huge quantities of overburden waste rocks (named herein PLW) which contain significant quantities of carbonates (calcite (46 wt %) and dolomite (16 wt %). The column experiments were set-up in laboratory and the testing were run under anoxic and oxic conditions by using a hydraulic retention time was 15 hours. The inflow to the treatment system ranged 5.5 mL/min, with acidic pHs of around 3, concentrations of dissolved Fe, Mn, Al, Ca, Zn and Cu were 600, 20,166, 350, 15 and 23 mg/L respectively, containing also some traces of Co, Cr and Ni. The test results showed that pH became neutral and a significant decrease in terms of metal concentrations; in particular for Fe (600 to 120 mg/L), Al (160 to 1.7 mg/L) and Cu (23 to 0.002 mg/L)

One-Dimensional Consolidation Parameters Of Cemented Paste Backfills

Each year, mine and mill operations generate enormous amounts oftwo waste types – fine-grained tailings and coarse-grained waste rocks. Fine-grained tailings are either discharged in slurry form to surface tailings dams or delivered in cementitious form to underground mine stopes as backfilling, while coarse-grained rocks are typically stored by depositing as a dry material in large dumps. The engineering design of surface tailings dams or underground mine stopes is often controlled by the high compressibility and low shear strength characteristics of fine-grained tailings. Cemented paste backfill CPB indicating saturated, fine-grained backfills can undergo major consolidation settlement during early curing stages. Thus, a better understanding ofthe rate and magnitude ofboth differential and total settlement ofCPB cured under stress is essential for a proper backfill geotechnical design. The consolidation parameters of CPB can be determined from an improved lab setup called CUAPS (curing under applied pressure system). This setup is capable of simulating the CPB placement and curing conditions, and measuring the consolidation parameters of CPB cured under effective stresses ranging between 0.5 and 400 kPa. In this study, a series of one-dimensional consolidation tests were conducted on CPB samples allowing for examination of the effects of binder type and rate as well as curing time on the compression properties (e.g., coefficient of consolidation cv, compression index Cc, and recompression index Cr) and the final geotechnical index properties (e.g., void ratio ef, water content wf, and degree ofsaturation Sf). Results showed that as the binder content increases, the initial resistance to consolidation increases. The cv value decreases over the course of time due to evolution of the CPB microstructure generated by the hydration process

Editorial for Special Issue “Towards a Sustainable Management of Mine Wastes: Reprocessing, Reuse, Revalorization, and Repository”

The mining industry continues to face many challenges due to its potential environmental impacts [...

CIL Gold Loss Characterization within Oxidized Leach Tails: Creating a Synergistic Approach between Mineralogical Characterization, Diagnostic Leach Tests, and Preg-Robbing Tests

A double refractory gold ore contains gold particles locked in sulphides, solid-solution in arsenopyrite, and preg-robbing material such as carbonaceous matter, and so on. The diagnostic leach test (DLT) and preg-robbing (PR) approaches are widely used to investigate the occurrence and the distribution of refractory gold. DLT serves to qualitatively evaluate the gold occurrences within the ore. Preg-robbing, or the ore’s capacity to fix dissolved gold, is evaluated to determine physical surface interactions (preg-borrowing) and chemical interactions (preg-robbing). The objective of this project is to characterize the refractory gold in Agnico Eagle Mine’s Kittilä ore using the DLT and PRT approaches coupled with mineralogical analyses to confirm testing. The studied material was sampled from the metallurgical circuit following carbon in leach (CIL) treatment at the outlet of the autoclave in order to investigate the effect of the autoclave treatment on the occurrence and distribution of gold. Different reagents were used in the DLT procedure: sodium carbonate (Na2CO3), sodium hydroxide (NaOH), hydrochloric acid (HCl), and nitric acid (HNO3). The final residue was roasted at a temperature of around 900 ◦C. These reagents were selected based on the mineralogical composition of the studied samples. After each leaching test/roasting, cyanide leaching with activated carbon was required to recover gold cyanide. The results show that gold is present in two forms (native and/or refractory): to a small extent in its native form and in its refractory form as association with sulfide minerals (i.e., arsenopyrite and pyrite) and autoclave secondary minerals that have been produced during the oxidation and neutralization processes such as iron oxides, iron sulfates, and calcium sulfate (i.e., hematite and jarosite), along with carbonaceous matter. The results of DLT indicate that 25–35% of the gold in the tails is nonrecoverable, as it is locked in silicates, and 20–40% is autoclave products. A regrind can help to mitigate the gold losses by liberating the Au-bearing sulphide minerals encapsulated within silicates

Prediction of acid mine generating potential: Validation using mineralogy

peer reviewe

Desulfurization of the Old Tailings at the Au-Ag-Cu Tiouit Mine (Anti-Atlas Morocco)

Tailings from the abandoned Tiouit mine site in Morocco are mainly composed of sulfides, hematite, and quartz. They contain 0.06–1.50 wt % sulfur, mostly in the form of pyrite, pyrrhotite, and chalcopyrite. The tailings also contain gold (3.36–5.00 ppm), silver (24–37 ppm), and copper (0.06–0.08 wt %). Flotation tests were conducted to reprocess the tailings for Au, Ag, and Cu recovery, and at the same time to prevent acid mine drainage (AMD) generation through the oxidation of sulfide minerals, including pyrite, sphalerite, arsenopyrite, chalcopyrite, galena. The flotation results confirmed that environmental desulfurization is effective at reducing the overall sulfide content in the tailings. The recovery of sulfides was between 69% and 75%, while Au recovery weight-yield was between 2.8% and 4.7%. The test that showed the best sulfur recovery rate and weight-yield was carried out with 100 g/t CuSO4 (sulfide activator) and 50 g/t of amyl xanthate (collector). The goal of this study was also to assess the remaining acid-generating potential (AP) and acid-neutralizing potential (NP) of the desulfurized tailing. The geochemical behavior of the initial tailings sample was compared to that of the desulfurized tailings using kinetic weathering cell tests. The leachates from the desulfurized tailings showed higher pH values than those from the initial tailings, which were clearly acid-generating. The residual acidity produced by the desulfurized tailings was most likely caused by the hydrolysis of Fe-oxyhydroxides

Valorization of Phosphate Waste Rocks and Sludge from the Moroccan Phosphate Mines: Challenges and Perspectives

Sedimentary phosphate mines produce millions of tons of waste rocks during their open-pit mining. In addition, during ore phosphate beneficiation, fluorapatite is separated from associated gangue minerals by a combination of successive mineral processing steps that involve crushing / screening, washing, and flotation. These operations generate large volume of tailings (called phosphate sludge) that are deposited in large surface ponds and waste rocks stockpiled within the mining site. The potential reuse of these phosphate mine by-products (waste rocks and sludge) has been investigated in the last 10 years. The first investigated option consisted in using the alkaline waste rocks (APW) to control the acid mine drainage (AMD). Indeed, these alkaline mine wastes contain significant quantities of calcite (46 wt%) and dolomite (16 wt%) that help in neutralizing the acidity generated by the wastes from the closed Kettara mine , located near Marrakech, Morocco. The addition of 15 wt% APW to the coarse Kettara tailings produced leachates with significantly lower acidity and metal loads in comparison to the unamended control sample. Secondly, the efficiency of APW was assessed in the laboratory as an alternative alkaline material for passive AMD water treatment. In semi-arid climate, the oxic passive treatment has been proven to be the most suitable. The pH of the water and its quality were significantly improved. As a third option, the hydrogeotechnical characterization of original and screened phosphate limestone waste rocks as well as the phosphate sludge showed their suitability for use as a component of store-and-release (SR) covers for industrial mine site reclamation. Lab tests (columns) and field tests (instrumented columns and experimental cells) showed that water infiltration can be controlled, even for extreme rainfall events (150 mm/day), by 1 m thick of a SR cover made with APW. Further research is currently being investigated around the recycling and valorization of phosphate sludge from phosphate mines as ceramics. Furthermore, the overburden of the phosphates sedimentary basins are mainly composed of marls; limestones blocks; silex bed; silex nodule; marls and clays; silicified limestone; which have a significant reuse potential as marble-mosaic floor, mortars and concrete, and natural stone products slabs for floors and stairs

Study of physico-chemical and mechanical characteristics of consolidated and unconsolidated cemented paste backfills

In recent years, it has been observed that the performance and quality of in situ cemented paste backfill (CPB) samples are constantly lower than samples obtained from the same CPB mix poured into laboratory-prepared plastic moulds. This could be well explained by the absence of an efficient laboratory tool capable of mimicking CPB's in situ placement, hardening, and curing conditions relating to stope size and geometry. To meet this need, a new laboratory tool named CUAPS (curing under applied pressure system) was manufactured and used to examine the effect of curing under effective stress on physico-chemical and mechanical properties of CPB, along with plastic mould samples. A comparative study was conducted for both CUAPS and mould samples containing a binder content of 3, 4.5, and 7 wt% after curing times of 7, 14, and 28 days. Results indicate that the performance of CUAPS-consolidated samples are always more realistic than those of plastic mould-unconsolidated samples mainly due to water drainage induced by consolidation. CUAPS has witnessed an advantageous effect on CPB hardening which includes the amount of bleeding water (separation of water from the fresh backfill material) and a combination of drainage of part of the mixing water and the settlement of paste backfill after its placement in the cap