Soilization utilization of solid waste: Ecological regulation of phosphorus tailings-based soil with physicochemical improvement and Bacillus_cereus-addition.

Extraction and utilization of effective phosphorus from solid waste have been an important approach for alleviating phosphorus resource shortage. The extraction of available phosphorus by microbial method with low cost, mild conditions and simple process has been drawing attention from the majority of research scholars. However, relevant studies on special microbial communities for effective phosphorus extraction from solid waste are less. In this work，a functional Bacillus_cereus strain screened from phosphate tailings, phosphate ore and forest rhizosphere soil was inoculated into phosphate tailings (PT), modified phosphate tailings (IS) and highland red soil (SS). Compared with SS, the water-holding properties, fertility, leaching toxicity and microbial community diversity of PT and IS with and without bacteria were analyzed. PT+, SS+ and IS+ (after adding bacteria to PT, SS and IS) showed moderately alkaline pH, and the available phosphorus content enhanced by 31.73%, 20.05% and 39.41% respectively. The leaching toxicity phosphate of PT+ and IS + decreased by 4.89 mg/kg and 2.61 mg/kg respectively, while that of SS + increased by 5.45 mg/kg, indicating differences in the phosphorus solubilization mechanism of Bacillus_cereus for different soils. Furthermore, the modification and bacteria treatment improved the relative abundance of Pedobacter, Alcaligenaceae and Pseudomonas, thus enhancing the phosphorus solubility of the PT bacterial community. This work may achieve efficient utilization and ecological restoration of phosphorus tailings-based soil and contribute to long-term sustainable agricultural development.

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.

Utilization path of bulk industrial solid waste: A review on the multi-directional resource utilization path of phosphogypsum.

Phosphogypsum is one of the hottest issues in the field of environmental solid waste treatment, with complex and changeable composition. Meanwhile, phosphogypsum contains a large number of impurities, thus leading to the low resource utilization rate, and it can only be stockpiled in large quantities. Phosphogypsum occupies a lot of land and poses a serious pollution threat to the ecological environment. This paper mainly summarizes the existing pretreatment and resource utilization technology of phosphogypsum. The pretreatment mainly includes dry method and wet method. The resource utilization technology mainly includes building materials, chemical raw materials, agriculture, environmental functional materials, filling materials, carbon sequestration and rare and precious extraction. Although there are many aspects of resource utilization of phosphogypsum, the existing technology is far from being able to consume a large amount of accumulated and generated phosphogypsum. Through the analysis, the comparison and mechanism analysis of the existing multifaceted and multi-level resource treatment technologies of phosphogypsum, the four promising resource utilization directions of phosphogypsum are put forward, mainly including prefabricated building materials, eco-friendly materials and soil materials, and new green functional materials and chemical fillers. Moreover, this paper summarizes the research basis of multi field and all-round treatment and disposal of phosphogypsum, which reduces repeated researches and development, as well as the treatment cost of phosphogypsum. This paper could provide a feasible research direction for the resource treatment technology of phosphogypsum in the future, so as to improve the consumption of phosphogypsum and reduce environmental risks.

Harmless treatment technology of phosphogypsum: Directional stabilization of toxic and harmful substances.

Phosphogypsum is one of the typical by-products of phosphorus chemical industry. As a strategic industry related to the national livelihood of China, phosphorus chemical industry has accumulated and produced a significant amount of phosphogypsum. In general, phosphogypsum contains approximately 80%-95% calcium sulfate dihydrate, and less than 5% toxic and harmful elements. In this paper, toxic and hazardous components in phosphogypsum were efficiently solidified and stabilized by highly targeted solidification and stabilization technology. Calcium carbide slag or lime was used as an alkali-base neutralizer of phosphogypsum, and polymeric ferric sulfate or polymeric aluminum chloride as a directional solidification stabilizer to analyze the leaching toxicity of the mixed powder in 1, 3, 5 and 15 days. The experimental results demonstrate excellent solidification and stabilization effect with the leaching pH of 6-9, the leaching concentration of P, F and heavy metals of less than 0.5 mg/L, 10 mg/L and 0.1 mg/L, respectively, which meets the requirements of relevant international standards. Mechanistic analysis indicates that the solidification and stabilization of toxic and hazardous substances in phosphogypsum is perfectly achieved owing to the generation, adsorption and encapsulation of insoluble substances. This technology can reduce the costs and difficulty in the phosphogypsum treatment, and has extensive application potentials.

Study of Semi-Dry High Target Solidification/Stabilization of Harmful Impurities in Phosphogypsum by Modification.

Phosphogypsum (PG) treatment is one of the research hotspots in the field of environmental protection. Many researchers both at home and abroad have devoted themselves to studies on harmless resource treatment of PG, but the treatment technology is unable to meet the demand of PG consumption due to the huge production and storage demands. In order to solve the problem of PG pollution, this study explored the different solidified effects of various modification formulations on the hazardous components in PG, using industrial solid waste calcium carbide slag (CCS) as an alkaline regulator; Portland cement (PC), polyaluminum chloride (PAC) and CaCl2 as the main raw materials of the solidification and stabilization formula and the water content in PG as the reaction medium. The results showed that CCS (0.5%), PC (0.4%) and PAC (0.3%) had a more significant solidified effect on phosphorus (P) and fluoride (F). PAC was added in two steps and reacted under normal temperature and pressure, and its leaching toxicity meets the requirements of relevant standards, which laid an excellent foundation for PG-based ecological restoration materials and filling materials, with low economic cost, simple process and strong feasibility. This will provide great convenience for the later mining and metallurgy.

Efficient purification of hydrogen cyanide by synergistic effects of electrochemical and liquid phase catalysis.

In this study, Co, Cu, Pd, and Pd/Cu composite metal ions were used to synthesize metal nanoparticles with high efficiency in purifying hydrogen cyanide gas. The pure liquid phase catalytic purification of hydrogen cyanide gas was studied. According to the removal rate, the Pd/Cu composite metal ions had the best purification efficiency among the nanoparticles of different metal types. The removal rate order was Pd/Cu>Pd>Cu>Co. The gas after reaction were analyzed by gas chromatography, and it was found that HCN was converted into CO2, N2 and NH3 by nanoparticles. Then, Pd/Cu composite metal ions with the highest purification efficiency were used to study the electrochemical synergistic liquid-phase catalytic purification of HCN gas. The effects of electrochemical conditions and current on the electro-hydraulic synergistic purification were studied. The removal efficiency of HCN by electrochemical synergistic liquid phase catalysis was better than that by pure liquid phase catalysis. The different nanoparticles before and after HCN absorption were characterized and analyzed to explore the purification process of HCN. The purification mechanism of hydrogen cyanide by Pd-Cu catalyst under applied voltage was studied under certain conditions. During the catalytic reaction, the nano-catalyst was partially dissolved in liquid phase and partially HCN reacts with metal ions on the free or nanoparticles to form complex [Mc(CN)n]2-n. Homogeneous and quasi-homogeneous reactions in liquid phase interweave together to form a more complex reaction system.

Adsorption of arsenic from aqueous solution using a zero-valent iron material modified by the ionic liquid [Hmim]SbF6.

The environmental and health impacts caused by arsenic (As) in wastewater make it necessary to carefully manage As wastes. In the present work, a composite of the ionic liquid [Hmim]SbF6 and nano-iron (H/Fe) was used as an adsorbent to remove As(v) from aqueous solution. To better understand the removal effect of H/Fe on As(v) in aqueous solution, the reaction parameters of pH, reaction temperature, time and H/Fe dosage were systematically analyzed in detail. The results show that H/Fe has significant removal efficiency toward As(v), and that the adsorption of As(v) by 0.5 g H/Fe reaches its maximum adsorption capacity within 2 h. The adsorption of As(v) on H/Fe is a non-linear, time-varying process. The initial adsorption reaction is fast; however, unlike at the beginning, the later reaction involves sustained slow absorption, resulting in a distinct two-phase adsorption characteristic. Redox reaction may be one of the mechanisms responsible for the slow adsorption of As(v) on H/Fe. At the same time, the As(v) removal effect of H/Fe is greatly restricted by the pH. Electrostatic adsorption, adsorption co-precipitation and redox reactions act together on H/Fe in the As(v) removal process. This study provides a basis for further clarifying the adsorption, adsorption rules and mechanism of As(v) on H/Fe and a feasible method for the improvement of As(v) removal efficiency of zero-valent iron materials.