Dissolution Of Aluminosilicates Research Articles

Relationship between MO/(SiO2+Al2O3) of materials—amorphous gel structure—properties of the one-part FA-Slag-based AAMs

The study investigates the impact of different amorphous gel structure by MO (CaO+Na2O)/(SiO2+Al2O3) ratios (specifically 0.66, 0.69, 0.73, 0.76, 0.84, and 0.90) on the fresh and hardened properties of one-part alkali-activated materials (OP-AAMs) derived from fly ash-slag. Unlike traditional two-part AAMs, the "just-add-water" preparation process of OP-AAMs facilitates the transition of geopolymer products from laboratories to the engineering field. Higher (CaO+Na2O)/(SiO2+Al2O3) ratios in fresh pastes promote the dissolution of active aluminosilicate in the alkali-activators, resulting in the formation of Si-rich gel with low-Al amorphous gel. This leads to reduced setting time, increased fluidity, and the occurrence of a viscoelastic phenomenon in the fresh properties. Throughout the geopolymerization process, the main product with the shortest mean chain length and higher Si/Al ratios is the C-(N)-A-S-H and N-A-S-H gel in the (CaO+Na2O)/(SiO2+Al2O3)=0.76 composition, which exhibits the highest 28-day compressive strength of 46 MPa. The findings highlight the potential of OP-AAMs and provide insights into the adjustment mechanism of MO/(SiO2+Al2O3) ratios to optimize the properties of OP-AAMs for engineering applications.

Preparation of one-part geopolymers using coal gasification slag: Effect of alkali fusion product additive and liquid/solid ratio

In this work, one-part geopolymers were synthesized through the alkali fusion and component additive method (AFCAM), utilizing coal gasification slag as the primary raw material. The investigation delved into the influence of varying fusion product contents and liquid/solid (L/S) ratios on the geopolymer properties. The experimental results demonstrated a non-linear correlation between the increase in fusion product content and the compressive strength of geopolymers, revealing an initial ascent followed by a subsequent decline. Additionally, a lower L/S ratio of 0.3 was observed to enhance compressive strength compared to the L/S ratio of 0.4. Notably, the optimal combination of an L/S ratio of 0.3 and a fusion product percentage of 30 % resulted in a remarkable compressive strength of 25.2 MPa. The comprehensive strength analysis suggested that an adequate amount of fusion product enhances the geopolymerization reaction, evidenced by the transformation of aluminum coordination states. Specifically, the conversion of five-coordinated and six-coordinated aluminum in slag to four-coordinated aluminum in geopolymers was observed. Concurrently, increased silicon and aluminum reactivity led to the formation of a robust Q4(4Al) network in the geopolymer gel. The impact of L/S ratios was attributed to the accelerated dissolution and hydrolysis of aluminosilicates at an elevated L/S ratio of 0.4, hindering polycondensation. These outcomes underscore the pivotal role of fusion product content and L/S ratio in governing the strength development of one-part geopolymers.

Gallium distribution in the Dulong Sn polymetallic deposit, SW China

The Dulong Sn polymetallic deposit is located in the SE Yunnan-West Guangxi ore province, and represents one of the three largest cassiterite-sulfide deposits in China. The deposit is a potential gallium (Ga) deposit in China with abundant tin and zinc resources. However, the occurrence of Ga in the deposit and the control on its mineralogy are still poorly understood. Here, we provide a detailed account of the gallium distribution in silicate, oxide, and sulfide minerals at Dulong, based on field geological and petrographic observations and geochemical analysis. Gallium is mainly hosted in Al-rich minerals, such as muscovite (avg. 139 ppm), biotite (avg. 86.8 ppm), and feldspar (avg. 21.3 ppm), in the ore-related granite. This distribution behavior of gallium is consistent with its predicted partitioning between the phenocrysts and melt. In the Sn ore, chlorite has high Ga content (avg. 104 ppm), probably caused by the gallium tends to form hydroxyl complexes. In contrast, pyroxene and sphalerite have low Ga content (avg. 1.24 and 1.50 ppm, respectively). Meanwhile, two types of magnetite (Mag-I and Mag-II) have been identified based on mineral paragenesis: Mag-I is mainly associated with sphalerite. It is porous, with the pores filled with Ga-rich aluminosilicates (e.g., chlorite), and has high Ga content (avg. of 18.3 ppm). Mag-II is mainly associated with sphalerite, pyrrhotite, and chalcopyrite, and has low Ga (avg. 1.34 ppm). The dissolution of Ga-rich aluminosilicates in magnetite likely provided gallium to magnetite, resulting in higher Ga content in Mag-I. The magnetite Ga content decrease with increasing distance from the mineralization center, and the magnetite mineralization temperature also shows a similar trend. This study confirms that the dominant substitution for Ga in muscovite is Ga3+ ↔ Al3+, and in magnetite it is Ga3+ ↔ Mn2+ + Me+ and Ga3+ ↔ Cu+ + Zn2+. Most of the Ga is hosted in chlorite and magnetite in the highly chloritized sulfide ore at Dulong, which is a critical factor that can significantly affect the estimation of economically recoverable by-product elements in the sulfide ore.

Evaluation of the Potential of Metakaolin, Electric Arc Furnace Slag, and Biomass Fly Ash for Geopolymer Cement Compositions.

The widespread use of geopolymer cement (GPC) has been hindered by a lack of scientific knowledge that still exists regarding its synthesis process. Key points, such as the release of aluminosilicate species from the raw materials and its link to the properties of GPC, have still not been completely studied. As a result, most of the GPC formulations covered in the literature are based on precursors' elemental analysis using XRF (X-ray Fluorescence), or other equivalent analysis methods, and consider that the total aluminosilicate content of the precursors is available for participating in the geopolymerization process, which seems very unlikely. In this study, the amounts of aluminate and silicate species released from metakaolin (MK), electric arc furnace slag (EAFS), and biomass fly ash (BFA) in alkaline dissolution tests were determined by simple spectrophotometric methods. It was found that MK yields the highest aluminosilicate dissolution amount, about 2.1 mmol of silicate + aluminate per gram of MK, while EAFS and BFA yield about 0.53 and 0.32 mmol/g precursor, respectively. These results were used to estimate the total amounts of dissolved aluminosilicates in a series of GPC mortars prepared from these raw materials, which were thereafter subjected to mechanical tests. It was shown that the mortars' compressive strength (which ranged from 1 to 63 MPa) is linearly correlated with their estimated total amount of dissolved aluminosilicates, with the best linear fit yielding a coefficient of determination above 0.99. It was concluded that by using the results of the dissolution tests, the estimation of compressive strength is greatly improved when compared to using the elemental analysis obtained by XRF, which yields a coefficient of determination of 0.88 and a larger dispersion of data points. The results reveal the usefulness of this simple method for evaluating the potential of inorganic industrial waste streams as precursors for GPC.

Mineralogy and geochemistry of pattern formation in zebra rock from the East Kimberley, Australia

Rhythmic patterns are widespread in geological materials. A particularly striking, macroscale example is zebra rock from the East Kimberley region of northwestern Australia. The rock is famous for its distinctive, rhythmically ordered, iron-oxide pattern, which transforms an Ediacaran-aged siltstone into an attractive semi-precious gemstone. Several different formation mechanisms of this pattern have been proposed in previous studies, with the two most prominent being redoximorphic banding in acid-sulfate soils and Liesegang banding in an acidic hydrothermal system. Using a combination of mineralogy, geochemistry and geological context, this study attempts to confirm both the occurrence and relative timing of acid-sulfate fluid rock interactions in zebra rock and seeks to determine whether pedogenic processes or hydrothermal alteration can better explain the origin of these patterns. We present the first evidence that the iron-oxide banding developed simultaneously with a period of aluminosilicate dissolution, clay precipitation, and fluid flow, consistent with the infiltration of an acidic fluid. This conclusion was evidenced through the hexagonal-platelet morphology of the hematite pigment, kaolinite-hematite textural relationships, and a paleoflow direction preserved in the asymmetric intensity of the hematite concentration. However, while the mineralogy of zebra rock strongly suggests interactions with acid-sulfates, the origin and temperature of the fluid could not be conclusively determined. Supporting a hydrothermal origin, a thorough analysis of zebra rock mineralogy revealed a mineral assemblage consistent with advanced argillic hydrothermal alteration, wherein pyrophyillite, kaolinite, and dickite indicate minimum palaeotemperatures upwards of 120 °C and the presence of alunite and a svanbergite-woodhouseite solid solution suggests oxidising, acidic (pH <5) conditions. The low Rb/Sr ratio and relative immobility of rare earth elements in most zebra rock deposits are also consistent with an acidic hydrothermal origin. Further support was also observed in the mineralogical trends between examined outcrops, grading from alunite-type to kaolinite/dickite-type facies in a south-west direction. But despite this evidence, the acid-sulfate soil hypothesis could not be refuted and was itself supported by the large number of pyrite dissolution voids both underlying and within the patterned layer. Furthermore, the consistent compaction of reduction spheroids, dissolution voids, and pseudomorphic inclusions within the light banding of zebra rock are in agreement with near-surface supergene weathering, ruling out hypogene hydrothermal alteration. A mechanism of pattern formation is proposed whereby zebra rock banding is formed by the Liesegang phenomenon, driven by the oxidation of Fe2+ ions during the infiltration of an Fe2+-rich, acid-sulfate fluid into oxidising host sediments.

Geochemical transformations of sulfur in salt lakes (Transbaikalia)

The water column in brackish and saline lakes hosts various forms of sulfur including sulfide (hydrosulfide), elemental, thiosulfate, and sulfate sulfur. The unequal distribution of these reduced sulfur species indicates the presence of two opposing processes - sulfate reduction and oxidation of newly formed hydrogen sulfide. The scale of these processes varies among lakes, resulting in differing proportions of reduced sulfur forms. The bacterial reduction of sulfate ions is confirmed by a significant separation of sulfur isotopes into sulfide and sulfate ions, with the lighter isotope accumulating in the former and heavier isotope in the latter. In most soda, chloride, brackish, and salt lakes, sulfate reduction is the principal process responsible for relatively low sulfate ion content. Additionally, the presence of an oxidizing environment and sulfides in host rocks provide additional sources for sulfates, leading to the formation of sulfate-type lakes. The formation of specific types and subtypes of brackish and salt lakes is determined by processes such as water evaporation, dissolution of aluminosilicates, sulfate reduction, and oxidation of sulfides. The dominance of these processes contributes to the geochemical diversity of lakes.

Rare-Earth Elements Extraction from Low-Alkali Desilicated Coal Fly Ash by (NH4)2SO4 + H2SO4.

Coal fly ash (CFA) obtained from pulverized coal furnaces is a highly refractory waste that can be used for alumina and rare-earth elements (REEs) extraction. The REEs in this type of CFA are associated with a mullite and amorphous glassy mass that forms a core-shell structure. In this research, it was shown that complete dissolution of amorphous aluminosilicates from the mullite surface with the formation of the low-alkali mullite concentrate prior to sulfuric acid leaching with the addition of (NH4)2SO4 helps to accelerate the extraction of REEs. The extraction degree of Sc and other REEs reaches 70-80% after 5 h of leaching at 110 °C and acid concentration of 5 M versus less than 20% for the raw CFA at the same conditions. To study the leaching kinetics of the process, the effects of temperature (90-110 °C), liquid-to-solid ratio (5-10), and leaching time (15-120 min) on the degrees of Al and rare-earth elements (REEs) extraction were evaluated. After 120 min of leaching at 110 °C and L/S ratio = 10, the extraction of Al was found to be lower than 30%. At the same time, total REEs (TREE) and Fe extraction were greater than 60%, which indicates that a part of the TREE was transferred into the acid soluble phase. After leaching, the residues were studied by laser diffraction (LD), X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy (SEM-EDS) to evaluate the leaching mechanism and the solubility of Al- and Fe-containing minerals, such as mullite, hematite, and amorphous aluminosilicate.

Description of Si and Al Release from Aluminosilicate in the Acidic Condition Using Density Functional Theory: Protonated Terminal Oxygen

The molecular clusters ((HO)3Si-O-Si(OH)3 and (HO)3Al-O-Si(OH)3) representative of aluminosilicate mineral surface were employed to study the dissolution of aluminosilicate in acidic condition via density functional theory (DFT) with the M06-2X+G(d,p) methodology. The surface termination sites (Si and Al) were both tetra-coordinated and the terminal oxygen was protonated in an acidic condition. In the dissolution reaction, the calculated barrier height of the six-membered ring transition state complex containing two water molecules was predicted to be 76.13 kJ/mol, lower than that of the four-membered ring transition state complex containing one water molecule. The barrier height of the reaction decreased to 6.17 kJ/mol and was 91.90% lower than that for the Siter-O-Si without protonation. In addition, the calculated barrier heights for Al-terminated sites were predicted to be 22.23 kJ/mol, lower than those for the Si-terminated sites, suggesting that breaking the Al-O bond is easier than the Si-O bond in the aluminosilicate mineral surface. With the fracture of Si-O and Al-O bonds, the Si and Al release from the aluminosilicate. The results indicate that the acidic condition facilitates the release of Si and Al from the aluminosilicate, and the concentration of Al leaching from the aluminosilicate is higher than the Si.

Controllable Orientation Growth of ZSM-5 for Methanol to Hydrocarbon Conversion: Cooperative Effects of Seed Induction and Medium pH Control.

The growth orientation of ZSM-5 zeolites strongly affects product selectivity in methanol conversion reaction. Here, we proposed a versatile synthetic strategy by introducing seeds and controlling medium pH to achieve controllable orientation growth of ZSM-5. The systematic analysis of the crystallization process indicated that the introduction of seeds ensured successful crystallization in a quasi-neutral solution and the dissolution rate of seeds and aluminosilicate determined the growth orientation of ZSM-5. In the quasi-neutral solution, the slow dissolution of seeds and aluminosilicate enhanced growth advantages along the c axis. The ratio between the length of the c axis and b axis (Lc/Lb) of the obtained ZSM-5 at pH of 7 could reach 8.1, much higher than 1.8 obtained at pH of 11. No obvious impact of seed added amount on growth orientation was found, while with increasing seed crystal size, the obtained ZSM-5 showed preferred growth along the c axis. The Lc/Lb of the sample adding seeds with a size of 355 nm reached 7.9, much higher than 2.1 of the sample adding seeds with a size of 70 nm. The obtained ZSM-5 with specific growth orientation exhibited potential shape selectivity in methanol to aromatics and olefin reaction. This work opens new possibilities to tailor the orientation growth of ZSM-5 based on the seed-induced strategy under mild conditions.

Microstructural evolution of amorphous self‐healing geopolymer composites containing alumina and glass frit

AbstractGeopolymer refers to a large group of nanoporous, nanoparticulate materials that are synthesized by dissolution and polycondensation of aluminosilicates in basic solutions and can be made from a variety of starting materials, such as industrial waste ash, volcanic rock, or calcined clay. Geopolymers are X‐ray amorphous, corrosion resistant, refractory, and made at ambient temperature and pressure similar to cements. In this study, potassium metakaolin‐based geopolymer (KGP) composites containing alumina platelets and glass frit were fabricated, and the impact of heating temperature, dwell time, and heating/cooling rate on the microstructure was studied. The composites, heat treated up to 900°C for up to 20 h using heating/cooling rates of up to 1°C/min, showed that the addition of alumina platelets prevented major microcracking and was also able to reduce linear shrinkage. Glass frit has been shown to heal microcracks formed during KGP dehydration and crystallization. The resulting material had an open porosity of less than 1% and a uniform surface glaze of 250 μm thickness, while Oswald ripening of round closed pores occurred due to the migration of molten glass in the system.

Salicylic acid–methanol extraction of aluminosilicate hydrates

AbstractThis study focuses on understanding how salicylic acid and methanol (SAM), commonly used to dissolve certain calcium silicates in portland cement, affect geopolymer gels and other sodium aluminosilicate hydrates. The technique has been used in the past to selectively dissolve hydrated calcium silicates formed through alkali activation of aluminosilicate mixtures containing calcium in the expectation that the extraction does not dissolve alkali aluminosilicate hydrates. However, the work presented here reveals that SAM solution does, in fact, dissolve aluminosilicate hydrates. Zeolite A, a three‐dimensional, low‐silica, crystalline sodium aluminosilicate hydrate, was fully dissolved upon SAM extraction, zeolite X was partially dissolved in the SAM extraction, and only zeolite Y was completely unaffected by SAM extraction. Similar behavior was observed with amorphous sodium hydroxide‐metakaolin geopolymer products—at an early age (1 day), SAM dissolved all the gel and left only unreacted metakaolin, and at a later age (7 days), SAM partially dissolved the geopolymer gel. Nuclear magnetic resonance spectroscopy indicated that dissolution requires the presence of silicon at the Q4(4Al) sites. Extraction was seen to involve some dealumination and complete removal of sodium. The mechanism of aluminosilicate dissolution in SAM appears to be acid attack followed by removal of aluminum via chelation with salicylic acid.

Water chemistry variation in tropical high‐mountain lakes on old volcanic bedrocks

AbstractWater chemistry and its ecological implications have been extensively investigated in temperate high‐mountain lakes because of their role as sentinels of global change. However, few studies have considered the drivers of water chemistry in tropical mountain lakes underlain by volcanic bedrock. A survey of 165 páramo lakes in the Cajas Massif of the Southern Ecuador Andes identified 4 independent chemical variation gradients, primarily characterized by divalent cations (hardness), organic carbon, silica, and iron levels. Hardness and silica factors showed contrasting relationships with parent rock type and age, vegetation, aquatic ecosystems in the watershed, and lake and watershed size. Geochemical considerations suggest that divalent cations (and related alkalinity, conductivity, and pH) mainly respond to the cumulative partial dissolution of primary aluminosilicates distributed throughout the subsurface of watersheds, and silica and monovalent cations are associated with the congruent dissolution of large amounts of secondary aluminosilicates localized in former hydrothermal or tectonic spots. Dissolved organic carbon was much higher than in temperate high‐mountain lakes, causing extra acidity in water. The smaller the lakes and their watersheds, the higher the likelihood of elevated organic carbon and metals and low hardness. The watershed wetland cover favored metal levels in the lakes but not organic carbon. Phosphorus, positively, and nitrate, negatively, weakly correlated with the metal gradient, indicating common influence by in‐lake processes. Overall, the study revealed that relatively small tropical lake districts on volcanic basins can show chemical variation equivalent to that in large mountain ranges with a combination of plutonic, metamorphic, and carbonate rock areas.

What do relationships between extractable metals and soil organic carbon concentrations mean?

AbstractAluminum (Al)‐bearing and iron (Fe)‐bearing minerals, especially short‐range‐ordered (SRO) phases, are thought to protect soil organic C (SOC). However, it remains methodologically challenging to assess the influence of Al vs. Fe minerals or metal complexes. Whereas SRO Al and Fe phases share some properties, Al dissolved by oxalate (Alox) often correlates stronger with SOC than Fe dissolved by oxalate (Feox) or citrate–dithionite (Fecd). To further evaluate these relationships, we analyzed a large North American soil dataset from the National Ecological Observatory Network. A strong relationship between Alox and SOC (and weaker Feox‐SOC relationship) persisted even after excluding soils rich in SRO minerals (Andisols and Spodosols). Al dissolved by oxalate was strongly correlated with citrate–dithionite‐extractable Al (Alcd; slope = 0.92, R2 = .69), and discrepancies could be explained (R2 = .87) by greater dissolution of Al‐substituted Fe phases by citrate–dithionite and greater dissolution of aluminosilicates by oxalate. Aluminum dissolved by oxalate and Alcd were both strong SOC predictors despite their differing relationships with silicon (Si). Al dissolved by oxalate and Siox strongly covaried (R2 = .79), but Alcd was inconsistently related to Sicd (R2 = .18). Similar relationships of Alox and Alcd with SOC, despite differences in minerals extracted by oxalate and citrate–dithionite, suggest that Al‐OC complexes (as opposed to aluminosilicate or iron‐bearing minerals) were the best SOC predictor. This raises important questions: do Al‐OC complexes indicate protection from decomposition or simply reflect greater intensity of mineral weathering by organic acids; and, if the latter, then perhaps SOC input is driving Alox and SOC correlations rather than Al phase composition or abundance.

Evolution of a natural pozzolan-based geopolymer alkalized in the presence of sodium or potassium silicate/hydroxide solution

The present work studied the effect of the type of alkali on the structural evolution of a natural pozzolan from Hidalgo, México, alkalinized with sodium or potassium solution to obtain geopolymers. The Pozzolan is composed of clinoptilolite-type zeolite, calcite, and quartz. The alkali solution was a mixture of silicate/hydroxide of sodium or potassium with a volume ratio of 12. Alkali solution/pozzolan weight ratio was 0.6, and curing was at 25 °C. The geopolymerization reaction from the natural pozzolan alkalized to geopolymer was followed at different stages by isothermal calorimetry showing that the sodium solution promotes higher aluminosilicates dissolution from the pozzolan than the potassium one, and the condensation step is favored to allow the generation of interconnected structures. This step is delayed at intermediates curing times at the presence of potassium solution due to the less dissolution of aluminosilicates and the loss of water observed by FT-IR analysis, consequently slowing down the evolution of compressive strength at this curing time. The alkalized pozzolan produces a gel identified by the amorphous halo at 2θ < 10° and between 20°-40° 2θ in the XRD patterns. This gel is characteristic of the presence of geopolymer. The final geopolymer microstructure shows the morphology of thick plates. The compressive strength of the geopolymers at 28 days shows similar values (±10.8 MPa) independent of the type of alkali solution used, although this evolved differently.

Synthesis of Pervious Geopolymer from Coal Fly Ash and Bagasse Fly Ash for Copper Removal

Geopolymer has recently gained popularity as an eco-friendly material because of its potential to valorize waste. It is a new class of inorganic material formed upon dissolution of aluminosilicate in the presence of an activating solution. The aluminosilicate minerals become reactive and then form into aluminosilicate oligomers. While most of the study in geopolymer research is focused on cement and concrete industry, it also gained attention as an alternative material for solving environmental pollution in water. This study thus explores the use of combining coal fly ash and bagasse fly ash as the aluminosilicate source to produce pervious geopolymer for the treatment of copper-contaminated water. While coal fly ash (CFA) is a by-product of a coal-fired power plant, bagasse fly ash (BFA) is a waste product of the co-generation plant of sugar mills from burning bagasse. These raw materials were mixed with coarse aggregates and activating solution composed of sodium hydroxide and sodium silicate to produce a pervious geopolymer. The effects of the mix proportions of CFA and BFA on the compressive strength, porosity, and permeability of pervious geopolymer were investigated. Moreover, the copper removal efficiency of pervious geopolymer was determined using atomic absorption spectroscopy (AAS). The findings revealed that pervious geopolymer is a promising material that could remove copper at 67–87% efficiency.

On Using Si to Unravel Potential Sources of Dissolved Al to the Deep Arctic

AbstractAn examination of the vertical profiles of aluminum, silicic acid, and the Si:Al ratio indicates that the enrichment of dissolved Al in the bottom waters of the Arctic basins cannot be explained by the water column remineralization of vertically transported biological material. Instead, it is suggested that the bottom water enrichments are a result of the dissolution of amorphous aluminosilicates that are produced within the sedimentary pore waters by a reverse weathering process. We suggest that these materials are released into the low Si, low Al overlying water column by turbidity currents descending from the broad Arctic shelves which deliver sediments, water, and the products of reverse weathering into the bottom waters of the Arctic basins. It is suggested that from its delivery point at the basin edges, this dissolved Al signal then spreads out, enriching the signals in the bottom of the basins and mixes upward into the overlying water column to produce the observed vertical gradients. Thus, the deepwater Al enrichment is driven by a concentration gradient from below, that is, it is a bottom up (sedimentary driven), rather than the top down (particle export) process that has been previously suggested. It is also suggested that this dissolved Al signal might potentially be used as a tracer of these sporadic turbidity events, which in addition to transporting sediments, also are a mechanism for subducting water into abyssal regions. The observation of elevated dissolved Al signals at other ocean boundaries adjacent to Al‐rich lithogenic materials further suggests that the formation of the products of reverse weathering within sediments is probably widespread along continental margins.

Trace metals and metalloids and Ga/Al ratios in grey shale weathering profiles along a climate gradient and in batch reactors

Shale is an important lithology globally due to its wide spatial abundance and potentially high trace metal and metalloid (TMM) geochemistry, which can be potentially inherited by its overlying soils. Unlike other soils, shale-derived soils inherit organic matter and oxides (Fe and Mn) which promote accumulation and retention of both geogenic and exogeneous TMMs. Here, we explore TMMs in seven grey shales weathering profiles along a north–south transect spanning the western flank of the Appalachian Mountains from New York to Tennessee. Overall, total TMM concentrations in the grey shales and their soils were below concentrations known to be toxic and below concentrations observed in black shales. Tau values show that shale-derived soils are net accumulators of many TMMs (As, Cd, Co, Cu, Ni, Pb, Sb, Sn and Zn) but others (Cr, W, and V) showed a net depletion. Many of the TMMs had high proportions (5–50%) that were sequestered in reducible phases (amorphous and crystalline Fe oxides) but few TMMs were associated with oxidizable phases (organic matter, reduced minerals). Sulfides and oxides (Mn nor Fe) were not detected by X-ray diffraction (<2% g/g). TMM accumulation and release during weathering was not extensively related to climate or soil development/age as we hypothesized, potentially due to localized effects of vegetation, geomorphology, pollution, and physicochemical parameters of the shale. Our laboratory batch reactor experiments indicated that some TMMs had highest release rates under oxic, acidic conditions with organic acids present (Cr, Ga, Sn, Sb, and W) implying aluminosilicate dissolution control or under slightly acidic, reduced conditions (As, Cd, Co, Cu, Ni, Pb, V, and Zn), suggesting association with geogenic oxides. Total Ga/Al ratios in rock to soil profiles were not varying significantly across the climate-soil development gradient, despite batch reactor acidic conditions generating low Ga/Al ratios. This implies weathering of shales is dominated by processes that do not fractionate Ga/Al ratio (organic or inorganic colloid production) as our laboratory results suggests oxic, acidic aluminosilicate weathering should generate a high Ga/Al solid phase.

Influence of molarity and alkali mixture ratio on ambient temperature cured waste cement concrete based geopolymer mortar

Generation of an enormous amount of construction and demolition (C&D) waste due to rapid growth in the infrastructure segment globally is a matter of dire concern for the present decade due to poorly managed disposal to re-utilization. The present study focuses on the formulation of an effective utilization regime of C&D waste (cement concrete) for its re-consumption as geopolymer mortar. Formulation of different molarities of sodium hydroxide (6 M to 16 M) and alkali mixture ratio of sodium silicate to sodium hydroxide solution (1.5, 2.5 and 3.5) have been done and cured for 90D at controlled ambient temperature. The samples were tested for fresh and hardened properties. The effect of silicate modulus and Na2O% with different alkali proportions on the hardened properties were studied. The results reveals that the optimum compressive strength of 20.7 MPa is achieved at a silicate modulus of 1.54 and Na2O% of 12.5%. Further microstructural analysis (mineralogical, elemental, thermal and bonding types) has been done to better comprehend the interactive performance of C&D waste with the change in alkali quantities. The physicochemical and microanalysis reveals that molarity, dissolution of aluminosilicates, and mineralogical compositions are the main factors governing the outcomes while keeping the curing regime at ambient temperature.

Quantifying aluminosilicate manganese release and dissolution rates across organic ligand treatments for rocks, minerals, and soils

Quantifying aluminosilicate manganese release and dissolution rates across organic ligand treatments for rocks, minerals, and soils

The waste rock of the Touro copper deposit in Galicia, Spain: challenges for its environmental characterization

Characterization of metamorphic rocks to evaluate waste material acid rock drainage potential is particularly challenging as commonly used laboratory methods can result in its significant underprediction. Static tests were conducted for over 300 samples from the Touro copper project and indicate that carbon-based methods frequently overestimate acid neutralization potential due to the presence of both graphite and manganese–iron carbonates. The Modified Sobek method more accurately accounts for the buffering capacity of carbonates and does not account for graphite, although aluminosilicate dissolution kinetics need to be evaluated in the context of sulfide oxidation rates. Historic sulfur assays for the project relied on methods insufficient to fully digest metamorphosed sulfides and required correction. The more aggressive Leco method provides accurate sulfur estimates and has now been adopted for the project. Static test metrics such as the net neutralization potential or neutralization potential ratio, therefore, can give misleading results when incorrect characterization methods are employed. Such metrics should be considered as screening level, used with caution, and complemented with careful field and laboratory kinetic tests. Preliminary humidity cell testing of five Touro samples suggests that terminal pH values for cells that have become acidic closely match predicted net acid generation (NAG) pH values. The NAG pH test avoids some of the challenges associated with sulfur and carbon predictions in metamorphic rocks as it directly buffers sulfide oxidation acidity with available material neutralization potential. As such, NAG pH has been adopted as the accepted project metric for segregating acid-generating from non-acid-generating waste. Supplementary material: All Touro project static and kinetic test data are available at https://doi.org/10.6084/m9.figshare.c.5389948 Thematic collection: This article is part of the Hydrochemistry related to exploration and environmental issues collection available at: https://www.lyellcollection.org/cc/hydrochemistry-related-to-exploration-and-environmental-issues