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Soil is formed through the weathering of natural rocks, and the solid composition of soil is at least 90% minerals. Soil experiences acidification and heavy metal contamination, and these phenomena are global problems that must be addressed on the basis of green chemistry principles to achieve sustainable agricultural development and maintain a healthy ecological environment. Soil may be effectively remediated by applying mineral-based soil conditioners. In this study, soil formation was simulated and a novel nano-submicron mineral-based soil conditioner was prepared from a potassium-rich feldspar by using an environmentally friendly hydrothermal method to buffer severe acidification and inhibit the phytoavailability of hazardous elements in soil. Field and in-house experiments confirmed that the performance of the proposed soil conditioner as soil amendment was effective. Soil pH was improved by 1%e9% compared with that of the control group, and soil bulk density decreased by approximately 8%. Al concentration in soil decreased by 29%e42% compared with that of the control group, and this observation indicated that aluminum toxicity was alleviated. Cd concentration in the corn of the rice also decreased by 50% compared with the control level, and this result suggested that cadmium accumulation was inhibited. This excellent performance was attributed to multifactor synergy and closely related to the morphology, chemical composition, mineral components, and preparation method of the proposed soil conditioner.

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An artificial silicate composite material prepared by the hydrothermal reaction of K‐feldspar and lime, showed excellent performance in remediating the soil. To elucidate the physicochemical properties of the artificial silicate composite material, K‐feldspar and lime were reacted in mild hydrothermal conditions (T=190 °C; P∼12.4 atm; t=0∼36 h). The hydrothermal product was systematically investigated using various techniques such as X‐ray powder diffraction (XRPD), scanning electron microscopy, and inductively coupled plasma‐optical emission spectrometry (ICP–OES). Quantitative evaluation of the extent of reaction by ICP–OES and XRPD methods enabled the analysis of hydrothermal evolution with prolonged time. The hydrothermal treatment of K‐feldspar with lime exhibits complex product phases, including leftover K‐feldspar, calcium hydroxide, calcite, grossular, tobermorite, alpha‐dicalcium silicate hydrate, potassium carbonate, bütschliite, and amorphous calcium silicate hydrate. The analysis of the reaction reveals that the K‐feldspar dissolution showed a clear transition, with the hydrothermal reaction beginning to slow down after 20 h. The slowdown of the K‐feldspar dissolution was essentially caused by different reaction kinetics and mechanisms before and after 20 h. The study yields vital and valuable insights into comprehending the chemistry and mineralogy of the artificial silicate composite material and producing a multielement reservoir from potassium‐rich rocks.

To elucidate the physicochemical properties of the artificial silicate composite material, K-feldspar and lime were reacted in mild hydrothermal conditions (different reaction temperatures and various K-feldspar/lime ratios). Formed phases were investigated using various techniques, such as X-ray powder diffraction, the Rietveld method, scanning electron microscopy (SEM), and inductively coupled plasma-optical emission spectrometry. The analysis revealed that tobermorite, grossular (hydrogarnet), alpha-dicalcium silicate hydrate (α-C2SH), amorphous calcium silicate hydrate, potassium carbonate, bütschliite, calcite, and calcium hydroxide formed with various conditions. Both the temperature and the Ca/Si molar ratio in the starting material greatly affected the formation of phases, especially the generation of tobermorite and α-C2SH. The substitution of H4O4 ↔ SiO4 proceeded with the increase of the Ca/Si molar ratio rather than the reaction temperature and the reaction time. More hydrogen was incorporated in hydrogarnet through the substitution of H4O4 ↔ SiO4 with the increase of the Ca/Si molar ratio in the starting material. Due to the properties of tobermorite as a cation exchanger and its potential applications in hazardous waste disposal, experimental parameters should be optimized to obtain better performance of the artificial silicate composite material from K-feldspar and lime hydrothermal reaction. The dissolution mechanism of K-feldspar was also discussed.

Cd contamination of rice in recent years has aroused a nationwide concern on the potential health risk to people in China. A significant increase of soil acidification in major Chinese croplands improves available Cd content by crops, and this further pushes a heavier burden on controlling Cd contamination. Therefore, it is urgent to find a workable and green way to control Cd contamination, i.e., decrease Cd content in rice, for people's health in China, as other countries in the world. From chemical and economic points, stabilizing/solidifying Cd may be a feasible way except in-situ ways such as removing it by the absorption of special plants and ex-situ ones such as removing the contaminated soil and treating it by special equipment. Then, it is very important how to choose a green solidifying agent. By simulating a rock-weathering process, a nano-submicron mineral-based soil conditioner (NSC) was prepared through environmentally friendly hydrothermal reaction. The application of NSC not only decreased Cd content in rice, i.e., inhibited Cd absorption, and increased pH of the soil, but also improved the content of healthy nutrients such as organic matter, available Ca, available K, available P, and available Si in the soil. The mechanism why NSC showed such good performance was also discussed in this study.

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