Wastewater irrigation: An opportunity for improving soil phosphorus availability; PHREEQC modeling and adsorption studies

Heavy metals release in lead-zinc tailings: Effects of weathering and acid rain

Heavy metals (HMs) release from lead (Pb)-zinc (Zn) tailings poses significant environmental risks to surrounding areas. Furthermore, with the natural weathering and frequently happened acid rain events, the release of HMs could be elevated. This study conducted a series of laboratory column experiments with thermodynamics and hydrogeochemical analysis to investigate the environmental behavior of HMs release in Pb-Zn tailings under natural weathering conditions and acid rain events. Results showed that the weathering of calcite facilitates the release of Pb (17.9 mg/kg) and cadmium (Cd) (0.15 mg/kg), while acid rain promotes Zn release (10.5 mg/kg) from the Fe-Mn oxides, with no significant change for arsenic (As). Among the influencing factors during the column experiments, the oxidation-reduction potential (ORP) was identified as the primary indicator for the predictions of the HMs release behavior based upon the Random Forest model (R2 = 0.973 - 0.997). Correlation analysis revealed a strong relationship between coexistent ions and HM release patterns. Therefore, saturation index (SI) could effectively identify the influence range of each mineral phase on HM release. This study provides scientific evidence for effective management in carbonate-type tailings ponds.

Adsorption characteristics of Ag+ on sphalerite surface: a combined experimental and first-principle study

The rapid development of industrial society is also accompanied by the generation of a large amount of heavy metal wastewater, which has caused serious harm to the ecological environment and human society. Natural sphalerite has an important value in the environmental field due to its own semiconducting properties. In order to effectively remove Ag+ from wastewater containing silver, this study develops a natural mineral-based Ag+ adsorbent material (sphalerite) based on elemental affinity qualities and mineralization principles. The results of batch experiments showed that the initial Ag+ concentration of 50 mg/L reduced to 0.094 mg/L with a reaction duration of 15 min, a sphalerite dose of 5 g/L, an initial particle size of -400 mesh (38 μm), a reaction temperature of 25 °C, and a pH of 5. The highest adsorption capacity is 19.77 mg/g, and the adsorption behavior is consistent with the Freundlich isotherm model and pseudo-second-order adsorption kinetics. The results of solution chemical analysis indicate that the presence of Ag+ is primarily influenced by the presence of S2-. Further analysis using SEM-EDS, FTIR, and XPS techniques reveals that Ag+ is chemically adsorb onto the mineral surface, resulting in the formation of Ag2S. DFT calculations further confirm the overlap between the Ag 4d orbitals and the S 3p orbitals on the surface of sphalerite, further confirming its chemical adsorption. Mulliken populations suggest that charge transfer occurs between Ag+ and S atoms in the sphalerite surface. This research systematically reveals the Ag+ adsorption mechanism on sphalerite surface and expands research ideas for treating heavy metal wastewater.

Aluminium sulfate synergistic electrokinetic separation of soluble components from phosphorus slag and simultaneous stabilization of fluoride

In this study, fluoride (F) was stabilized and soluble components, namely phosphate (P), K, Ca, Cr, Mn, and Pb, were extracted from phosphorus slag (PS) by using aluminum sulfate (AS) synergistic electrokinetic. PHREEQC simulation was used to determine the occurrence form of each ion in the PS. The mechanisms by which various electrokinetic treatment methods affected conductivity and pH distribution were carefully investigated. Electrokinetic treatment increased P concentration of the anode chamber from 22.7 mg/L to 63.39 mg/L, whereas K concentration increased from 15.26 mg/L to 93.44 mg/L. After AS-enhanced electrokinetic treatments, the concentrations of the different components were as follows: P, 131.66 mg/L; K, 198.2 mg/L; and Ca, 331.3 mg/L. The removal rate of soluble P in PS slices increased to 80.88% by 1.5 V/cm of treatment, and it increased to 94.04% after AS enhancement treatment. For water-soluble F, the removal rate from the PS slices in the anode region was 86.03%, decreasing F concentration in the electrode chamber to 9.57 × 10^-3 mg/L. Different extraction efficiencies and stability levels of each component in the PS were regulated at various electrode regions by using different processes such as electromigration, electro-osmotic flow, flocculation, and precipitation. Good results can be obtained if fluoride is solidified concurrently with the removal or recovery of P, K, Ca, and other elements using 2%-4% AS enhanced electrokinetic treatment. Furthermore, CaSO₄·2H₂O whiskers were produced in the electrode regions when AS content was 6%. The findings of this study indicated that the AS synergistic electrokinetic method is suitable for stabilizing F and removing heavy metals from PS, thus providing a promising technology for recycling valuable components such as P, K, Ca, and Sr and for the simultaneous production of CaSO₄·2H₂O whiskers. This study provides insights for developing novel technologies for the clean treatment and high-value utilization of PS.