Minerals

Slawsonite’s (SrAl₂Si₂O₈) structure evolutions depending on temperature (27–1000 ℃) have been studied by in situ single-crystal X-ray diffraction. The SrO₇ polyhedron expands regularly with the temperature increase. Silicon and aluminum cations are ordered in tetrahedral sites of the studied slawsonite; no significant changes in their distribution as temperature increases were observed. Slawsonite demonstrates a relatively high volume thermal expansion (α_V = 23 × 10^–6 °C^–1) with high anisotropy, typical for framework feldspar-related minerals and synthetic compounds. It was found that, contrary to previously published data, the crystal structure of slawsonite is stable in the studied temperature range and no phase transitions occur up to 1000 °C. The role of Ca and Ba substitution for Sr and Al/Si ordering on polymorphism of natural MAl₂Si₂O₈ (M = Ca, Sr, Ba) is herein discussed. Full article

The uptake of beryllium by hardened cement paste (HCP, with CEM I 42,5 N BV/SR/LA type) in degradation stage I was investigated with a series of batch sorption experiments with 10⁻⁶ M ≤ [Be(II)]₀ ≤ 10^−2.5 M and 2 g·L⁻¹ ≤ [S/L] ≤ 50 g·L⁻¹. All experiments were performed under Ar atmosphere at T = (22 ± 2) °C. Solubility limits calculated for α-Be(OH)₂(cr) in the conditions of the cement pore water were used to define the experimental window in the sorption experiments. Beryllium sorbs strongly on HCP under all of the investigated conditions, with log R_d ≈ 5.5 (R_d in Lkg⁻¹). Sorption isotherms show a linear behavior with a slope of ≈ +1 (log [Be(II)]_solid vs. log [Be(II)]_aq) over four orders of magnitude (10⁻⁸ M ≤ [Be(II)]_aq ≤ 10⁻⁴ M), which confirm that the uptake is controlled by sorption processes and that solubility phenomena do not play any role within the considered boundary conditions. The similar uptake observed for beryllium in calcium silicate hydrate (C-S-H) phases supports that the C-S-H phases are the main sink of Be(II) in cement. The strong uptake observed for Be(II) agrees with the findings reported for heavier metal ions, e.g., Zn(II), Eu(III), Am(III), or Th(IV). The exceptional sorption properties of beryllium can be partially explained by its small size, which result in a charge-to-size ratio (z/d) of the same order as Eu(III) or Am(III). Kinetic experiments confirm the slow uptake of Be(II), which is characterized by a two-step process. In analogy to other strongly sorbing metal ions such as Zn(II) or Th(IV), a fast surface complexation (t < 4 days) followed by a slower incorporation of Be(II) in the C-S-H structure (t ≥ 60 days) are proposed. The surface complexation was studied in detail with molecular dynamic simulations, and the most common surface species are identified and described. This work provides the first experimental evidence supporting the strong uptake of Be(II) by HCP in degradation stage I, further extending previous findings on C-S-H phases and HCP in degradation stage II. These results overcome previous conservative estimates assuming no or only a weak uptake in cementitious systems and represent a relevant contribution for the quantitative assessment on the retention/mobilization of beryllium in the context of nuclear waste disposal. Full article

S- and Fe-cycling bacteria can decisively affect the crystallization of Fe-bearing minerals in sediments from fluvial environments. We have studied the relationships between the Fe-bearing mineral assemblage and the bacterial community composition in the sediments rich in organic matter from the upper Chicamocha river basin (Colombia). Rapid flowing sections of the river contain sediments that have a high redox potential, are poor in organic matter and are enriched in kaolinite and quartz. On the other hand, the mineral assemblage of the sediments deposited in the La Playa dam with a high content in organic matter is enriched in Fe-bearing minerals: a) vivianite and pyrite in the permanently flooded sediments of the dam and b) pyrite and goethite in the periodically emerged sediments. The bacterial community composition of these sediments reveals anthropic organic matter pollution processes and biodegradation associated with eutrophication. Moreover, periodically emerged sediments in the La Playa dam contain bacterial groups adapted to the alternation of dry and wet periods under oxic or anoxic conditions. Cell-shaped aggregates with a pyritic composition suggest that sulfate-reducing bacteria (SRB) communities were involved in the precipitation of Fe-sulfides. The precipitation of vivianite in the flooded sediments was favored by a greater availability of Fe(II), which promoted the iron-reducing bacteria (IRB) enrichment of the sediments. The presence of sulfur-oxidizing bacteria (SOB) in the flooded sediments and the activity of iron-oxidizing bacteria (IOB) in the periodically emerged sediments favored both pyrite crystallization under a high sulfide availability and the oxidation of microbially precipitated monosulfides. Moreover, IOB enhanced goethite formation in the periodically emerged sediments. Full article

The Lutang graphite deposit in Chenzhou, Hunan province, China, is a well-known coal seam-derived graphite (graphite formed from coal during its natural evolution) deposit with proven reserves of 9.5 million tons and prospective reserves of around 20 million tons (2015 data). The graphite occurs at an andalusite bearing sericite quartz chlorite metamorphic mudstone around a c. 530 km² Qitianling granite intrusion. A set of coal seam-derived graphite samples from the Lutang graphite deposit in Hunan was examined by geochemical, crystallographic, and spectroscopic techniques to assess changes in the degree of graphitization approaching the intrusion. The carbon content, degree of graphitization, and Raman spectral parameters of series coal seam-derived natural graphite samples show a fluctuating increase with increasing proximity to the granite intrusion. The profile of geological structural features has a close spatial correlation with the variations in the degree of graphitization of series coal seam-derived natural graphite, and a strain-enhanced graphitization model is proposed. Moreover, the geographical distribution and the degree of graphitization are positively related to changes in the iron content of chlorite, suggesting a graphitization process promoted by mineral catalysis during metamorphism. A close spatial relationship exists between graphite mineral and chlorite occurrences when approaching the intrusive mass. The results of this research are important for understanding the role of tectonic stress and mineral catalysis on the genesis of coal-derived graphite. Full article

Manganese oxides occur in a wide range of environmental settings either as coatings on rocks, sediment, and soil particles, or as discrete grains. Although the production of biologically mediated Mn oxides is well established, relatively little is known about microbial-specific strategies for utilizing Mn in the environment and how these affect the morphology, structure, and chemistry of associated mineralizations. Defining such strategies and characterizing the associated mineral properties would contribute to a better understanding of their impact on the local environment and possibly facilitate evaluation of biogenicity in recent and past Mn accumulations. Here, we supplement field data from a Mn rock wall deposit in the Ytterby mine, Sweden, with data retrieved from culturing Mn oxidizers isolated from this site. Microscopic and spectroscopic techniques are used to characterize field site products and Mn precipitates generated by four isolated bacteria (Hydrogenophaga sp., Pedobacter sp., Rhizobium sp., and Nevskia sp.) and one fungal-bacterial co-culture (Cladosporium sp.—Hydrogenophaga sp. Rhizobium sp.—Nevskia sp.). Two of the isolates (Pedobacter sp. and Nevskia sp.) are previously unknown Mn oxidizers. At the field site, the onset of Mn oxide mineralization typically occurs in areas associated with globular wad-like particles and microbial traces. The particles serve as building blocks in the majority of the microstructures, either forming the base for further growth into laminated dendrites-botryoids or added as components to an existing structure. The most common nanoscale structures are networks of Mn oxide sheets structurally related to birnessite. The sheets are typically constructed of very few layers and elongated along the octahedral chains. In places, the sheets bend and curl under to give a scroll-like appearance. Culturing experiments show that growth conditions (biofilm or planktonic) affect the ability to oxidize Mn and that taxonomic affiliation influences crystallite size, structure, and average oxidation state as well as the onset location of Mn precipitation. Full article

The article addresses the issue of mining and industrial waste stored in tailings and heaps in mining areas, and it explores the existing, as well as new, ways of reducing its harmful impact on the environment. On the basis of the Russian experience in mining industry in Ural, it presents a process which makes it possible to eliminate the amassed hazardous waste, retrieve the valuable material (metals) stored in it, and use the remaining waste as backfill in order to both: store it underground (and not on the surface) and prevent the disasters caused by the collapse of the abandoned shafts, thus prolonging the functioning of the mining areas. The process includes preliminary activation treatment of materials found in industrial waste in a disintegrator to protect the environment from toxic pollution. The promising results of the experiment have been discussed, taking into account the complexities of economic evaluation of the idea. Full article

Remarkable hydrostatic pressures have a significant effect on the failure mechanical properties of seafloor minerals, which also affects the selection and development of mining excavation tools. In this paper, a Brazilian splitting test and triaxial compression test were adopted to investigate the strength and deformation behavior of two kinds of seafloor massive sulfides (SMS) samples at a small-scale size. Based on the mineralogical characterization of the studied samples, the mechanical properties were preliminarily correlated with their internal structures and mineral compositions. Results indicate that there is a significant difference in the triaxial compression deformation properties between the two kinds of SMS samples and the geotechnical data are controlled by mineral type and composition, including porosity. In general, the triaxial compression process of the two kinds of samples included initial compaction, elastic stage, yield stage, failure stage and residual stage, and shows strain softening characteristics after the peak. With the increase in confining pressure, the strain-softening behavior of the white sample is mitigated and gradually changes into strain-hardening. The peak strength and peak strain of the two samples increased linearly with the increase in confining pressure within the confining pressure range of these tests, and the failure pattern of the specimens also changed from a typical brittle failure to a ductile failure. The results of this study provide data to support further understanding of different kinds of SMS, and are of great significance in the design of efficient SMS exploitation equipment. Full article

Identifying the proper chemical and biological materials as soil amendments is a great concern because they replace soil properties and subsequently change the soil quality. Hence, this study was conducted to evaluate the effects of a diverse range of soil amendments including bentonite (B), talc (T), activated carbon (AC), and cornstarch (CS) in form of sole and composite on the immobilization and bioavailability of As, Cu, and Zn. The amendments were characterized by SEM, FT-IR, and XRF, and applied at 2% (w/w) in the experimental pots with an Asteraceae (i.e., lettuce) for 45 days to monitor plant growth parameters and soil microbial community. Soil pH from 6.1 ± 0.02 significantly increased in the amended soils with the maximum value found for TAC (7.4 ± 0.04). The results showed that soil amendments reduced easily in an exchangeable fractionation of As, Cu, and Zn with the maximum values found for BAC by 66.4%, AC by 84.2%, and T by 89.7% respectively. Adding B, T, AC, and their composites induced dry biomass of lettuce >40 wt.%, while CS and its composites did not affect the dry biomass of the plant. The average content of Cu and Zn in plant tissues decreased >45 wt% in B, AC, and their composites amended soils; meanwhile, AC and its composites mitigated As uptake by >30 wt.% in lettuce. The results of Biolog Ecoplate showed that the amending soils improved the microbial community, especially for composites (e.g., TCS). The results demonstrated that adding composites amendments provided an efficient method for the immobilization of metals and metalloids, and also induced plant growth parameters and microbial community. Full article

An essential operation in the mineral processing of copper ores into concentrates is blending, as it guarantees a constant feed for the flotation cells, increases metal recovery rate and reduces tailings. In this study, copper ores from Huelva province (Spain) were investigated by quantitative XRD (X-ray diffraction) methods to optimize blending and detect penalty minerals, which can affect flotation and concentrate quality. The Rietveld method in combination with cluster analysis, PLSR and more traditional chemical analysis provide a more complete and in-depth characterization of the ore and the whole process. The mineralogical monitoring can be fully automated to enable real-time decision making. Full article

The hybrid failure is a coupled failure mechanism under the action of tensile and shear stresses. The failure is critical in cemented paste backfill (CPB) since there are no visible signs prior to the failure. Few studies have been conducted on the coupled stress response of CPB. This is most likely due to a lack of suitable laboratory equipment and test procedures. This paper presents a new punching shear apparatus to evaluate the hybrid failure of CPB. We harness two-dimensional finite element analysis (FEA) for supplementing experimental study in providing stress transformation, deformation, and possible failure mechanisms. Our study suggests that the coupled stress is a combination of tensile and shear strength in function of the angle of the frustum. The strengths measured by the coupled stress are comparable to those measured by direct shear and tensile strength tests, in which the strength properties of CPB are curing time and binder content dependent. The FEA results substantiate the effectiveness of proposed model for predicting the hybrid failure of CPB. Full article

Thirty-eight samples of minerals from Paleoproterozoic Layered PGE Intrusion Monchepluton, located in NE Fennoscandia, were tested. An automated computational technique was used which involved counting the sides superimposed on vectorized graphics using separated crystal boundaries. The results were obtained for olivine, orthopyroxene, clinopyroxene, and plagioclase. On this basis, an interpretation of the mineral box fractal dimension was made, along with an interpretation of its nature in the rock in which it was found. The performed calculations were applied to the sampling positions, and maps of changes in fractal dimensions were prepared. The nature of the minerals studied was correlated with the type of rocks present in Monchepluton. Then, the fractal dimensions were scaled to a percentage scale determining the mean value for the euhedral crystal as 100%, and a map was obtained representing the advancement of secondary processes after summing these data for all four investigated minerals. This method was analyzed and its advantages and limitations shown. Full article

Due to the absence of early magma records in pegmatites, it is difficult to investigate the behavior of Nb and Ta during the transformation from magma to pegmatite melt. Zircon megacrysts in an NYF-type (Nb-Y-HREE-F) pegmatite from the Arabian Shield could be divided into three phases from core to margin. The Phase Ι zircon in the core of the zircon megacrysts had typical magma oscillatory zonation with ∑REE content from 300 to 400 ppm, Th/U ratios of less than 0.1 and Nb/Ta ratios of less than 1.0. Phase ΙΙ zircon had oscillatory zonation and was enriched with LREEs mostly with Th/U ratios of 0.1–0.2 and Nb/Ta ratios of 1.0–3.0. Phase ΙΙΙ unzoned zircon had the highest ∑REE content, from 8000 to 15,000 ppm, with Th/U ratios higher than 3.0 and Nb/Ta ratios higher than 5.0. The Hf-O isotopic composition was similar in the different phases of zircon with initial ¹⁷⁶Hf/¹⁷⁷Hf ratios of 0.28258–0.28277, εHf(t) values from 8.0 to 12.0 and δ¹⁸O_VSMOW from +4.0‰ to +5.0‰. Zircon megacrysts in the NYF-type pegmatite from the Arabian Shield record the transformation from magma to pegmatite melt. Similar Hf-O isotopic compositions mean a closed magmatic system without contamination by external melt, rock or fluid. The proposed modeling shows that magma with low Nb and Ta concentrations and Nb/Ta ratios could evolve into residual pegmatite melt with a high Nb content and superchondrite Nb/Ta ratio during several stages of melt extraction and fractional crystallization of Ti-rich minerals, such as rutile and titanite. The Nb/Ta ratio can be used as an effective indicator of the transformation process from magma to pegmatite melt. Full article

Soil organic matter (SOM) and various inorganic minerals represent key components of soils. During pedogenesis and due to biological activity these species interact, having a crucial impact on the formation of an aggregated soil structure with a hierarchical arrangement from nano to macro scale. In this process, the formation of organo–mineral microaggregates represents a dominant factor affecting soil functions and properties. This study focuses on the interactions between humic substances (HSs) and the mineral kaolinite as typical representatives of SOM and soil minerals. By performing classical molecular dynamics (MD) simulations on models of HSs and kaolinite, we demonstrate how two dominant but chemically different kaolinite surfaces affect the stability of HSs microaggregates. By analyzing volumetric, structural, and energetic properties of SOM–kaolinite models, we explain possible mechanisms of the formation of stable SOM–clay aggregates and show how a polarized environment affects the electrostatic interactions, stabilizing the microscopic structure of SOM–mineral aggregates. Our results showed that when stable aggregates of HSs are confined in kaolinite nanopores, their interactions with kaolinite surfaces disintegrate them into smaller subaggregates. These subaggregates are adsorbed more strongly on the polar aluminol surface of kaolinite compared to less the active hydrophobic siloxane surface. Full article

Phosphate rocks are a vital resource for world food supply and security. They are the primary raw material for phosphoric acid and fertilizers used in agriculture, and are increasingly considered to be a potential source of rare earth elements. Phosphate rocks occur either as sedimentary deposits or igneous ores associated with alkaline rocks. In both cases, the genesis of high-grade phosphate rocks results from complex concentration mechanisms involving several (bio)geochemical processes. Some of these ore-forming processes remain poorly understood and subject to scientific debate. Morocco holds the world’s largest deposits of sedimentary phosphate rocks, and also possesses several alkaline complexes with the potential to bear igneous phosphate ores that are still largely underexplored. This paper summarizes the main geological features and driving processes of sedimentary and igneous phosphates, and discusses their global reserve/resource situation. It also provides a comprehensive review of the published data and information on Moroccan sedimentary and igneous phosphates. It reveals significant knowledge gaps and a lack of data, inter alia, regarding the geochemistry of phosphates and basin-scale correlations. Owing to the unique situation of Moroccan phosphates on the global market, they clearly deserve more thorough studies that may, in turn, help to constrain future resources and/or reserves, and answer outstanding questions on the genesis of phosphates. Full article

The article presents the history of iron ore mining and production in present-day Poland and takes into account mining and production techniques and the influence of mining on the development of the surrounding areas. Examples of development are presented for the most important iron ore mining centers established since the period of the so-called Roman influences—Lower Silesia in the region of Tarchalice and the Świętokrzyskie region in the area of Góry Świętokrzyskie (Świętokrzyskie Mountains). The oldest traces of underground iron ore mining in Poland date back to the 7th–5th century B.C., and iron production dates back from the 1st century B.C. in the Częstochowa region where economically significant iron ore exploitation started in the 14th century and lasted until the 20th century. Studies showed that the development of iron ore mining in today’s Poland was associated with significant events in the country’s history, for example, with the expansion of a network of fortified castles in Silesia or with the industrial revolution. In each case, the increase in iron production resulted in the development and growth of the surrounding areas. Full article

The study of thermal conductivity anisotropy is of great importance for more accurate heat flow calculations, geodynamic studies, development and utilization of hot dry rock, and simulation of heat transfer in geological reservoirs of nuclear waste, and so on. To study the thermal conductivity anisotropy of rocks, 1158 cores from 60 boreholes in East China were tested for thermal conductivity, including thermal conductivity values parallel to (λ_∥) and perpendicular to (λ_⊥) structural planes of basalt, mudstones, gneisses, sandstones, carbonates, evaporites, and metamorphic rocks. The thermal conductivity anisotropy is not obvious for sand, clay, and evaporate, and the average anisotropic factors of 1.19 ± 0.22, 1.18 ± 0.17, and 1.18 ± 0.17 for tuff/breccia, granitoid and contact metamorphic rocks, respectively, indicate that these three rocks have strong anisotropy characteristics. Finally, the effect of thermal conductivity anisotropy on heat flow is studied and discussed in detail, showing that the results of thermal conductivity tests have a significant effect on the calculation of heat flow and thermal structure, and the data show that a deviation of about 10% in thermal conductivity causes a deviation of about 11% in heat flow, which may lead to a misperception of deep thermal structure studies. The regular and anisotropic characteristics of thermal conductivity of various rocks in Eastern China obtained in this paper can provide parameter support for projects such as heat flow calculations, thermal structure studies, and geothermal resource development and utilization. Full article

Waste electrical and electronic equipment or e-waste generation has been skyrocketing over the last decades. This poses waste management and value recovery challenges, especially in developing countries. Printed circuit boards (PCBs) are mainly employed in value recovery operations. Despite the high energy costs of generating crushed and milled particles of the order of several microns, those are employed in conventional hydrometallurgical techniques. Coarse PCB pieces (of order a few centimetres) based value recovery operations are not reported at the industrial scale as the complexities of the internal structure of PCBs limit efficient metal and non-metal separation. Since coarse PCB particles’ pre-treatment is of paramount importance to enhance metal and non-metal separations, thermal, mechanical, chemical and electrical pre-treatment techniques were extensively studied. It is quite evident that a single pre-treatment technique does not result in complete metal liberation and therefore several pre-treatment flowsheets were formulated for coarse PCB particles. Thermal, mechanical and chemical pre-treatments integrated flowsheets were derived and such flowsheets are seldom reported in the e-waste literature. The potential flowsheets need to be assessed considering socio-techno-economic considerations to yield the best available technologies (BAT). In the wider context, the results of this work could be useful for achieving the United Nations sustainable development goals. Full article

The town of Krugersdorp in South Africa is the locus of an important wildlife game reserve, the Krugersdorp Game Reserve (KGR), which is juxtaposed by the (<1000 m) down-gradient of the large-scale gold mining outfits of Mintails Mogale Gold (MMG) and Rand Uranium (RU). The aim of the study was to determine the concentration levels of potentially harmful elements (PHEs) that have accumulated due to post-mining activities in the local water bodies in Krugersdorp and to use these data as a prerequisite and basis for formulation of the most appropriate remediation measures. Thirty water samples were collected and analysed in situ for: water temperature, pH, dissolved oxygen (mgl⁻¹), dissolved oxygen (%), total dissolved solids (TDS), oxidation/reduction potential (ORP), and electrical conductivity (EC). This was later followed by laboratory analyses of aliquots of the water samples by ICP-MS for twelve PHEs whose concentration ranges were: As (0.70–32.20), Ag (0.16–105.00), Al (1.00–41.00), Co (0.07–6.16), Cr (1.60–5.00), Cu (0.80–8.00), Fe (23.00–117.00), Mn (0.14–12 255.00), Ni (0.20–7.00), Pb (0.80–6.30), V (1.90–55.20), and Zn (2.20–783.00). Areas of the town where excessive concentration levels of these elements have negatively impacted the health of its wildlife population and surrounding ecosystems are identified, and credible mitigation measures proffered. Full article

Deep-sea polymetallic nodules are a mineral resource with potential for commercial development. Due to the unique deep-sea environment in which they are found, specialized technology and equipment are required for their extraction. In this paper, firstly, the development of deep-sea polymetallic nodule mining technology is classified into three stages, and its characteristics are summarized. Moreover, the results from research into deep-sea polymetallic nodule mining technology are analyzed, including proposals for mining systems, research into key technologies, basic scientific problems, and proof of technical feasibility from sea tests. Secondly, the testing of the collector prototype and the environmental impact assessment study of Global Sea Mineral Resources NV, as well as the progress of the deep-sea polymetallic nodule mining test project in China, are introduced. On this basis, the opportunities and challenges brought by the fast-growing demand for electric vehicles to the development of deep-sea polymetallic mining technology is analyzed, and a possible technical scheme for a mining system and the trends in its development towards high reliability and high standards of environmental protection according to the requirements of commercial exploitation are explored. This provides a reference for the research and development of high-efficiency technology and equipment for the mining of deep-sea polymetallic nodules. Full article