Heavy metal being immobilised in the lattice of a mineral is beneficial for its removal, recovery and reuse from wastewater. It is therefore essential to determine how heavy metals can be transferred into minerals controllably. This work developed a potential way for transforming heavy metals (Cu2+, Pb2+, Ni2+, Zn2+ and Cd2+) in wastewater into solids with high efficiency by introducing crystal seeds. The results of this work demonstrate that the addition of hydrotalcite and paratacamite crystal seeds can enhance heavy metal removal, both in simulated and actual acid mine wastewater. The removal rate can be increased by 18–47% and 31.8% for each heavy metal and total heavy metals in the presence of each crystal seed, respectively. Additionally, the recovery products of heavy metals can be changed by crystal seeds. In the systems without crystal seeds, the recovery products are mixtures; but the pure phase can be achieved if crystal seeds are added. For instance, in the Cu2+–Al3+–Cl– system without crystal seeds, the products were mixtures of paratacamite and layered double hydroxides (LDHs). But the products could be altered easily by hydrotalcite or paratacamite seeds. Paratacamite seeds induced Cu2+ to form paratacamite at pH 5.0, but a mixture of LDHs and paratacamite at pH 7.0. In contrast, hydrotalcite seeds induced Cu2+ to form LDHs at both pH 5.0 and 7.0. From the perspective of enthalpies of formation, CuAl-LDH and paratacamite are potential products, but the former is generally more stable, and thus it becomes the dominant product of the reaction systems using crystal seeds. It is believed that the crystal seeds can accelerate the dynamic process of LDH formation. This work suggests a controllable way for heavy metals removal, recovery and reuse.

Five typical metal cations (i.e. Na+, K+, Ca2+, Mg2+ and Al3+) were selected as representatives to study the influence of metal cations on the dissolution and transformation of biotite. This work focussed on the mineralogical features of transformation products and phase transformation mechanisms by utilising modern spectroscopic methods and micro-beam characterisation techniques. In comparison with a control system, K+ inhibited the dissolution and transformation of biotite, leading to the generation of amorphous iron hydroxides on the biotite surface. Na+, Mg2+ and Ca2+ promoted the dissolution of biotite but inhibited its transformation into kaolinite, with the Na system producing sodium-bearing biotite, vermiculite, hematite and a small amount of kaolinite, and the Mg and Ca systems producing mainly vermiculite, chlorite and hematite. Al3+ notably accelerated the dissolution and transformation of biotite, resulting in well-crystallised kaolinite and hematite. Furthermore, metal cations changed the formation mechanism of kaolinite by altering the dissolution rate of biotite. Within the blank system, biotite dissolved slowly, with elements (i.e. Al and Si) accumulating on the biotite surface and growing epitaxially into kaolinite; whereas in the Al system, the rapid dissolution of biotite provided a large amount of Si, which combined with Al in the solution, forming kaolinite via a dissolution–recrystallisation process. In addition, the exchange reactions of metal-cation–K+ and the competitive adsorption of metal-cation–proton simultaneously constrained the dissolution process of biotite. This work offers a theoretical basis for an in-depth comprehension of the factors influencing biotite weathering and new insights into the evolution of clay minerals in terrestrial surface environments.

Nano-silicon has been regarded as the most promising anode material for next-generation lithium-ion batteries (LIBs). However, the preparation of nano-silicon suffers from high cost, complex procedures, and low yield, which hinders its commercial application. In this study, porous nano-silicon with particle sizes in the range of 50–100 nm was prepared through molten salt-assisted magnesiothermic reduction using porous nano-silica derived from clay minerals as the precursor. Through combining ball milling and acid activation, the synthesised nano-silica derived from montmorillonite exhibited smaller particle sizes (below 50 nm), higher specific surface area (647 m2 g–1), and total pore volume (0.71 cm3 g–1). This unique structure greatly facilitated the conversion efficiency of silica into nano-silicon by maximising the contact area between silica and magnesium powder and optimising the diffusion kinetics of magnesium atoms. When used as anodes in LIBs, the synthesised nano-silicon materials demonstrated a high specific capacity of up to 1222 mAh g–1 and an excellent capacity retention rate of 79% after 150 cycles at a current density of 0.5 A g–1. This method provides a novel approach for the cost-effective and large-scale production of nano-silicon materials for high-performance anodes.

Different two-dimensional structural units of layered silicate minerals have different chemical and reaction properties. Sulfuric acid solution mineral-leaching systems with pH of 2.0, 4.0 and 6.0 were constructed to investigate the differential dissolution properties of lizardite (1:1 type), chlorite and talc (2:1 type minerals) and the chemical kinetic mechanism of the mineral–water interface reaction. The results showed that the dissolution efficiency of Mg in lizardite is higher than that of chlorite and talc in acidic environments (pH of 2.0, 4.0 and 6.0). The dissolution efficiency of Mg in chlorite is greater than that of talc for acidic environments when pH is 2.0 and 4.0, but chlorite and talc have nearly identical Mg dissolution efficiencies at a pH of 6.0. This phenomenon is related to the defect site on the tetrahedral sheet of chlorite and is controlled by the change of the dissolution efficiency of Al. The dissolution rates of Mg and Si in lizardite, chlorite and talc decreased with the increase of reaction time in the acidic medium for pH = 2.0, 4.0 and 6.0, and there are two linear dissolution trends at different pH values. The dissolution efficiencies of Mg and Si in lizardite, chlorite and talc were simulated and predicted by establishing a logistic model. It was found that the maximum dissolution efficiency of 2:1 type minerals chlorite and talc are only 4.72% and 1.58%, which is much lower than that of 1:1 type lizardite. This research on the reaction mechanism and dissolution kinetics of lizardite, chlorite and talc not only helps to deepen the understanding of the mineral–water interface interaction, but also reveals the different rules for Mg, Si and Al dissolution in different types of trioctahedral mineral–water interface reactions, and provides a crystal chemical basis for the ion migration and action mechanism of minerals.

In the soil environment, divalent heavy metal ions often interact with trivalent metal ions to form hydrotalcite supergroup nanominerals (also known as natural layered double hydroxides, LDHs), effectively immobilising heavy metals within the minerals structure. Concurrently, these LDH minerals also show high surface reactivity and can adsorb surrounding heavy metal ions, thus they play a significant role in heavy metal pollution purification. However, the impact of the subsequent geochemical evolution of heavy-metal-containing LDHs on the migration and transformation of structural and surface-adsorbed heavy metals as well as its surface reactivity towards surrounding heavy metals remains unclear. Herein, Ni(II)Fe(III)-LDH and Co(II)Al(III)-LDH were taken as examples to reveal the influence of redox evolution on the immobilisation of structural and adsorbed heavy metals. The results of this work indicate that the oxidative–reductive alternating evolution of structural Ni, Fe and Co elements constrain the transformation of heavy metals, as well as their bioavailability greatly. The oxidative–reductive alternating evolution helped reduce the content of bioavailable heavy metals in exchangeable and carbonate-bounded states. It can also enhance the integration of heavy metals with the LDH structure and help transform heavy metals into residual states, thereby reducing their mobility and bioavailability. However, oxidative–reductive evolution significantly reduced the surface reactivity of LDHs, diminishing their interface locking ability for surrounding heavy metal ions. This research provides foundational data for assessing the long-term environmental performance of LDHs.

The environmental effects of nanoparticles have attracted widespread attention. The removal and recycling of nanoparticles are crucial for both environmental protection and resource reuse. However, current removal and recycling methods are not yet mature, and there is a need to explore inexpensive materials for the efficient removal and recycling of nanoparticles. This study investigates the effects of pyrite species, thermal modification temperature, pH and ionic strength on the adsorption of gold nanoparticles (AuNPs) by pyrite. The experimental results demonstrate that the adsorption rate of artificially thermally modified pyrite is slightly faster than that of naturally thermally modified pyrite. However, the concentration of Fe ions dissolved from the artificially thermally modified pyrite is higher. Natural pyrite, when thermally modified at 400°C and 500°C, adsorbs 100% of AuNPs within 10 min. The lower the acidity of the system, the faster the adsorption rate. Conversely, an increase in ionic strength decreases the adsorption rate. Artificially thermally modified pyrite primarily adsorbs AuNPs through electrostatic gravitational attraction, which is supplemented by a significant amount of chemisorption. After four recycling cycles, the adsorption and desorption rates of AuNPs using artificially thermally modified pyrite were 92.1% and 94.2%, respectively, indicating excellent adsorption and recovery performance. The results of this study provide a new method for the recycling of nanoparticles and an experimental basis for the further application of thermally modified pyrite in environmental treatments.

Sulfosalt assemblages in a specimen from the Boliden Au–Cu–(As) deposit in northern Sweden, comprise micrometre to nanometre scale intergrowths of Se-rich izoklakeite and tintinaite with average formulae and calculated homologue number (N) given as: (Cu1.88Fe0.18)2.06(Pb22.92Ag1.47Cd0.01Zn0.01)24.41(Sb13.12Bi8.69)21.8(S50.19Se6.43Te0.12)56.73, N = 3.83, and (Cu1.31Fe0.74)2.05(Pb10.58Ag0.18Cd0.05Zn0.02)10.83(Sb10.2Bi5.23)15.43(S32.22Se2.46)34.7, N = 2.05, respectively. Tintinaite coexists with (Bi, Se)-rich jamesonite. High-angle annular dark field scanning transmission electron microscopy (HAADF STEM) imaging reveals chessboard structures comprising PbS and SnS modules with the number of atoms in the octahedral (M) sites counted as: n1 = 18 and n2 = 8 for tintinaite and n1 = 30 and n2 = 16 for izoklakeite. The homologue number can be calculated using the formula: N = (n1/6)–1 and N = n2/4 for PbS and SnS modules giving NTti = 2 and NIz = 4. A new N = 3 homologue, defined by n = 12 and n = 24 SnS and PbS modules, respectively, is identified as single or double units within areas with intergrowths between kobellite and izoklakeite. HAADF STEM imaging also reveals features attributable to lone electron pair micelles within the Sb-rich kobellite homologues. Atomic-resolution EDS STEM chemical mapping of Pb–Bi–Sb-sulfosalts shows a correlation with crystal structural modularity. The maps also highlight sites in the SnS modules of tintinaite in which Sb > Bi. Coherent nanoscale intergrowths between tintinaite and izoklakeite define jigsaw patterns evolving from chessboard structures and are considered to have formed during co-crystallisation of the two phases. Displacement textures and crosscutting veinlets (a few nm in width) are interpreted as evidence for superimposed syn-metamorphic deformation and are associated with the redistribution of Bi and Se. Imaging and mapping using HAADF STEM techniques is well suited to characterisation of Pb–Sb–Bi-sulfosalt phases, offering largely untapped potential to unravel the evolution of chessboard structures with applications across mineralogy but also extending into allied fields.

The impact of temperature on the migration of cations within layers of clay minerals is of profound significance for the design and practical application of materials derived from clay minerals. This study focuses on Li+ and Na+ as representative cations, together with illite (Ilt) and montmorillonite (Mnt) as representative clay minerals. The study investigates the behaviour of cation migration and occupation within clay minerals across varying temperatures. A series of samples were prepared meticulously by immersing illite and montmorillonite in Li+ and Na+ solutions, subsequently subjecting them to different temperatures (unheated, 100, 150, 200, 250 and 300°C) for 24 h. Through the use of techniques such as X-ray diffraction (XRD), cation exchange capacity (CEC), Fourier-transform infrared spectroscopy (FTIR), magic angle rotating solid nuclear magnetic resonance spectroscopy (MAS NMR), and X-ray photoelectron spectroscopy (XPS), the study discerns structural transformations in illite and montmorillonite, and tracks the migration and occupation of Li+ and Na+. The findings reveal that following heating, Na+ and Li+ do not infiltrate the lattice of illite. For montmorillonite, Na+ also does not migrate into the montmorillonite lattice, however, in contrast, Li+ does exhibit migration into this lattice. Notably, the migration and occupation of interlayer Li+ within montmorillonite exhibit discernible temperature dependence. Specifically, upon reaching 150°C, interlayer Li+ migrate to ditrigonal cavities within the tetrahedral layers. As the temperature elevates to 200°C, Li+ further permeate vacant octahedral sites through the ditrigonal cavities, culminating in the formation of a localised trioctahedral structure.

Organic acids are commonly found in soils and sediments, playing an important role in the alteration and weathering of minerals and influencing a series of geochemical processes such as soil fertility, metal cycling and pollutant migration. In order to better comprehend the reaction mechanisms of different layered silicate minerals with organic acids, three minerals with various structure types, namely montmorillonite, kaolinite and muscovite, were investigated in this work. In particular, the effects of interfacial reactions with oxalic acid on the crystal structure, chemical composition, morphology and specific surface area of minerals were compared. The composition and structure of montmorillonite, kaolinite and muscovite during the interfacial reaction with oxalic acid were characterised using powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and inductively coupled plasma-optical emission spectroscopy (ICP-OES) methods. It was shown that Si4+ and Al3+ were dissolved gradually during the interfacial reactions and that the changes in the properties of minerals depended on structural characteristics. After 300 days of the interfacial reactions with oxalic acid, the dissolution percentages of Si4+ and Al3+ in montmorillonite, kaolinite and muscovite were 12.7%, 8.4%, 3.8% and 62.1%, 30.7%, 6.1%, respectively. Moreover, the lamellar morphology of montmorillonite was destroyed upon the interfacial reaction with oxalic acid, and irregular particles with sizes of ~100–500 nm were formed on the surface. The diameter of kaolinite flake particles decreased from 400–1500 nm to 50–400 nm, and the surface of rod-shaped particles was ruptured. The small particles disappeared from the muscovite surface, and the initially sharp edges became blunted. The specific surface area and the total pore volume of montmorillonite and kaolinite increased after the interfacial reaction with oxalic acid, whereas the opposite results were obtained for muscovite. The differential dissolution of the minerals during their interfacial reaction with oxalic acid was mainly related to the differences between cation occupancies, structural types, chemical bond strengths and specific surface areas.