通信作者：

王余莲（1986—），女，教授，博士，博士生导师，中组部“万人计划”青年拔尖人才，研究方向为矿物材料制备及功能化。E-mail：ylwang0908@163. com。

摘要：【目的】以菱镁矿为原料，制备具有良好吸附性能的大比表面积多孔羟基硅酸镁，推动菱镁矿资源高值化利用。【方法】通过煅烧-水化-碳化法将菱镁矿制成重镁水（Mg（HCO₃）₂）作为镁源，以正硅酸乙酯为硅源，采用水热法-煅烧法制备大比表面积多孔羟基硅酸镁；探究硅镁物质的量比、水热时间、水热温度及煅烧时间对产物显微结构、比表面积及孔径分布等的影响，采用X射线衍射仪、扫描电子显微镜、全自动比表面积分析仪、傅里叶变换红外光谱仪、X射线光电子能谱仪和电感耦合等离子体光谱仪对产物微观结构及吸附性能进行表征。【结果】当硅镁物质的量比为2：1、水热时间为8 h、水热温度为130 ℃，比表面积为630.36 m²/g，经过400 ℃、4 h煅烧后比表面积提高10.7 %，为706.28 m²/g，说明煅烧对比表面积提高有较大影响。多孔羟基硅酸镁的形成过程包括3个阶段：正硅酸乙酯水解生成富含硅羟基的环状多聚硅烷醇中间体；重镁水中镁离子与该中间体通过Si—O—Mg键交联组装为层状骨架；羟基占据层间与表面位点，稳定结构的同时并促进孔形成，煅烧活化使羟基硅酸镁内部脱水形成新的孔道。通过络合反应对重金属离子产生吸附作用，对Cu²⁺、Cr³⁺和Ni²⁺的最大吸附量分别为275、245、258 mg/g。【结论】以菱镁矿为原料制备多孔羟基硅酸镁，具有大的比表面积和良好的吸附性能，可应用于重金属离子吸附。

关键词：菱镁矿；羟基硅酸镁；多孔材料；比表面积；吸附

Abstract

Objective Using magnesite as the raw material, porous magnesium hydroxy silicate with excellent adsorption performance and large specific surface area is prepared to promote the high-value utilization of magnesite resources.

Methods Magnesite was converted into magnesium bicarbonate solution (Mg(HCO₃)₂) via calcination-hydration-carbonation process to serve as the magnesium source, while tetraethyl orthosilicate was used as the silicon source. Porous magnesium hydroxy silicate with a large specific surface area was then synthesized by combining the hydrothermal method with the calcination method. This study mainly investigated the effects of the molar ratio of silicon to magnesium, hydrothermal reaction time, hydrothermal temperature, and calcination time on the microstructure, specific surface area, and pore size distribution of the products. The microstructure and adsorption performance of the prepared products were characterized by means of XRD, SEM, BET, FTIR, XPS, and ICP-AES.

Results and Discussion Using magnesite as the raw material, magnesium bicarbonate solution prepared via the calcination-hydration-carbonation process was employed as the magnesium source, while tetraethyl orthosilicate served as the silicon source. Porous magnesium hydroxy silicate was synthesized using the hydrothermal method. When the molar ratio of silicon to magnesium was 2:1, the hydrothermal reaction time was 8 h, the hydrothermal temperature was 130 ℃, and magnesium hydroxy silicate product with a specific surface area of 630.36 m²/g was obtained. Among the synthesis parameters, the molar ratio of silicon to magnesium and the hydrothermal reaction time exerted the most significant effects on the specific surface area of the magnesium hydroxy silicate. During the reaction process, the magnesium silicate initially presented as bulk solids without obvious porous structures. With a gradual increase in the content of the silicon source, primary particles were observed to gradually emerge on the surface of the bulk magnesium silicate. As the hydrothermal time increased continuously, a highly developed porous network structure was finally formed. This phenomenon could be attributed to the more complete hydrolysis of tetraethyl orthosilicate resulting from the increased silicon source and extended hydrothermal time, which provided more silanol groups for the cross-linking reaction with magnesium ions and promoted the full assembly of the porous structure. In contrast, the hydrothermal temperature exerted a relatively significant influence on the product's aggregation state. When the hydrothermal temperature was appropriate， the product existed as bulk aggregates with well-defined pore channels and uniform particles. However, when the hydrothermal temperature was excessively high, the particles grew too fast, leading to their connection into sheet-like structures, the disappearance of pore channels, and a consequent decrease in specific surface area. The final product was identified as porous magnesium hydroxy silicate crystals with a granular accumulation structure. The calcination time also showed a notable impact on the specific surface area of the magnesium hydroxy silicate. The specific surface area reached a maximum value of 706.28 m²/g after 4 h of calcination, which was 10.7% higher than that of the uncalcined sample. Calcination could induce the removal of bound water molecules from the magnesium hydroxy silicate, thereby maintaining the pore channels while forming more mesoporous and microporous structures. However, excessively long calcination time might lead to pore channel collapse, resulting in structural damage and a subsequent decrease in specific surface area. Its formation process involved three stages: the hydrolysis of tetraethyl orthosilicate to generate cyclic polysilanol intermediates rich in silanol groups； the cross-linking assembly of ions from the magnesium bicarbonate solution with these intermediates into a layered framework via Si—O—Mg bonds; and the occupation of interlayer and surface sites by hydroxyl groups, which stabilized the structure and promoted pore formation, while subsequent calcination activation induced internal dehydration of the magnesium hydroxy silicate to form new pore channels. The product adsorbed heavy metal ions through complexation reactions, with the maximum adsorption capacities of 275, 245, and 258 mg/g for Cu²⁺, Cr³⁺, and Ni²⁺, respectively. The adsorption rate was fastest and the adsorption efficiency was highest within the first 5 min, after which the adsorption reached equilibrium. Meanwhile, the pseudo-first-order and pseudo-second-order kinetic models were employed to fit and analyze the adsorption data. The fitting results showed that the adsorption of the three heavy metal ions followed a chemical adsorption process, which was consistent with the previously proposed complexation reaction mechanism for heavy metal adsorption by porous magnesium hydroxy silicate.

Conclusion Porous magnesium hydroxy silicate prepared from magnesite possesses a high specific surface area and excellent adsorption performance, enabling its application in the field of heavy metal ion adsorption from polluted water. This study not only expands the methods for preparing magnesium silicate from mineral raw materials and supplements the specific reaction conditions, but also provides theoretical support and technical reference for the high-value utilization of magnesite resources and the development of efficient and low-cost heavy metal adsorption materials.

Keywords：magnesite; magnesium hydroxy silicate; porosint; high specific surface area; adsorption

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