Since ferric tetroxide (Fe₃O₄) has strong magnetic properties, coating amorphous silica (SiO₂) with Fe₃O₄ nanoparticles can protect the magnetic Fe₃O₄ particles and form a new magnetic adsorbent with a core–shell structure and small pore size, the strong magnetic properties of which can efficiently solve the problem of the difficult separation and recovery of heavy metals from wastewater affecting present-day adsorption techniques. In this paper, SiO₂-coated nanoscale Fe₃O₄ particles were prepared using a modified sol–gel method for the adsorption and removal of Cr(VI) at lower pollution concentrations. The adsorbent was characterized using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and a magnetic vibration sample magnetometer (VSM), and its adsorption performance was systematically investigated in terms of initial concentration, pH, and temperature. The experiments showed that the adsorption effect was optimal when the initial solution Cr(VI) was 40 mg/L. The adsorption capacity increased with a decrease in the initial solution’s pH and decreased with an increase in temperature. Furthermore, the adsorption capacity of Cr(VI) at low concentrations was much higher than that of other conventional adsorbents, the calculated unit adsorption capacity reached 13.609 mg·g⁻¹, and the removal rate reached 64.8%. In addition, the strong magnetic nanocomposite (MS) had excellent recoverability, could achieve desorption via alkaline washing, and retained about 75% of the initial adsorption capacity after six cycles.

In this study, we modify the Mobil Composition of Matter No. 48 (MCM-48) silica material (MCM-48-SH) using Mercapto. The preparation conditions of MCM-48-SH are then explored, its structural characteristics are analyzed using characterization, and it is used to adsorb Cr(VI) from wastewater. A series of experiments are then designed to adsorb Cr(VI) in experimental water, and the influence of solution environment changes (such as time, temperature, pH, and coexisting ions) on the adsorption effect was explored. The experimental data showed that the MCM-48-SH material not only retained the basic structure of MCM-48 but also successfully grafted the functional group -SH. The adsorption of Cr(VI) on MCM-48-SH followed the Langmuir isotherm model and the kinetic adsorption was fitted with a pseudo-second-order kinetic model. Under these conditions, the adsorption capacity of MCM-48-SH (17.9 mg/g) on Cr(VI) was much larger than that of unmodified MCM-48 (4.0 mg/g) and amino-modified MCM-48-NH₂ (0.5 mg/g). The adsorption effect was the most obvious when the pH = 2 but the adsorption effect was not good under alkaline conditions. Other competitive ions in the solution had an influence on the adsorption effect, among which anions had a great influence. Within 3 d, when the concentration of Cr(VI) was 80 mg/L, the maximum adsorption capacity reached 17.9 mg/g and the maximum removal rate reached 93.45%. In the comparative adsorption experiment, the adsorption effect of MCM-48-SH (17.9 mg/g) on Cr(VI) was notably better than that of the other two common adsorbents: coconut shell activated carbon (9.2 mg/g) and bentonite (1.2 mg/g). In summary, MCM-48-SH can be used to effectively eliminate Cr(VI) in waste water.

Establishment of geological model in volcanic area is challenging owing to lack of borehole data and the effect of volcanic activity on rock distribution. Taking full advantage of the existing complete volcanic landforms and recognized for seven eruptive cycles in Wudalianchi volcanic area, here we apply a layered approach to build geological models for meeting rapid development of agriculture and understanding the evolution of regional geological structure. Based on the volcanic eruption cycle, the stratas in Wudalianchi volcanic area are divided into four layers. UGrid (unstructured grid in GMS) is used combining with DEM data to hierarchically build 3D geological structure model of volcanic area, which realize the visualization of regional stratigraphic distribution, and the reliability of the model is verified by the formation mechanisms of different types springs. The stratified modeling provides a scientific and effective mean for the reconstruction of geological structure in volcanic areas where the data are short and the stratigraphic distribution is complex. The 3D geological structure model established can lay a foundation for the prediction, evaluation and sustainable use of regional groundwater, geothermy, mineral water and mineral mud resources.