Shi Lin,Zhan Cetao,Bai Wenjing,Wang Wei,Yuan Shoujun,Hu Zhen-Hu
Arsanilic acid ( p -ASA), an organoarsenic additive found in livestock wastewater, can release toxic inorganic arsenic into the environment. While bioelectrochemical systems have proven effective in decomposing organoarsenics, managing the resulting inorganic arsenic remains a challenge. This study demonstrated the feasibility of a two-stage bioelectrochemical process designed to facilitate p -ASA degradation and in situ recover inorganic arsenic from contaminated livestock wastewater. It consisted of two sequential stages: (I) anodic stimulation for p -ASA degradation and (II) reversing electrode polarities for the cathodic reduction of inorganic arsenic. In Stage I, the anode significantly enhanced the degradation of p -ASA, resulting in 18 μg/L of As(III) and 700 μg/L of As(V) released into the bulk solution. In Stage II, the cathode further reduced the As(III) and As(V) to 8.9 and 35.5 μg/L, respectively, through the synergistic action of the cathode and suspended microbes. The inorganic arsenic was recovered as a layer of As(V)-O on the cathode. Microbial analysis indicated that Alcaligenes was responsible for the degradation of p -ASA, while Anaerobacillus and Desulfitibacter played key roles in reducing As(V) and As(III) on the cathode, respectively. This study provided a promising alternative approach for the removal of organoarsenics and in situ recovery of inorganic arsenic from organoarsenic-bearing wastewater.
Heavy metal separation and recovery from hyperaccumulators are crucial to promote the industrialization of phytoremediation and prevent secondary heavy metal pollution. In this study, we developed an innovative modified steel slag/CaO 2 technology for arsenic recovery and separation via hydrothermal liquefaction (HTL) of As-enriched Pteris vittata L. (PVL). Arsenic migrated from the aqueous phase to the solid phase, with a recovery rate as high as 99.96 %, and the oxidation of arsenite was achieved with an impressive efficiency of 97.64 %. Experiments with model compounds revealed that the As in the PVL was immobilized by metal oxides (CaO, MgO, Fe 2 O 3 and SiO 2 ) in the modified steel slag and deposited in the solid phase. The coprecipitation of arsenic and heavy metals was verified via Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). As(III) was converted into As(V) via the strong oxidability of •OH and H 2 O 2 from CaO 2 . XPS confirmed that the interconversion of Fe 3+ and Fe 2+ significantly contributed to the oxidation and removal of arsenic. The concentration of As(III) in the system decreased to 1.96 % with this method. To investigate heavy metal recovery from the solid phase, magnetic experiments were subsequently conducted to investigate the arsenic distribution in the solid phase after magnetic separation. Notably, the As could be recovered in the magnetic solid phase, whereas 0.05 % of the As(III) and 18.46 % of the As(V) of the total arsenic were distributed in the non-magnetic solid phase. This study demonstrated that modified steel slag/CaO 2 has great potential for the detoxification and recovery of heavy metals in hyperaccumulators.
Graphical Sulfuric acid - hydrogen peroxide is used to leach containing-arsenic sulfide residue under the atmospheric pressure and mild temperature. Key factors of influencing the leaching process are investigated. Leaching rate for As is 98.42%. Arsenic(V) of leaching solution is reduced by SO 2 to obtain As 2 O 3 . The overall recovery rate of As throughout the entire process is 90.67%, thereby enabling the recovery of arsenic. Arsenic-containing sulfide residue from copper smelting is a kind of dangerous solid waste. However, the residue is also a recycling resource due to its numerous valuable components. Sulfuric acid-hydrogen peroxide was used to leach containing-arsenic sulfide residue, followed by the recovery of arsenic (As). The effects of temperature, dosage of hydrogen peroxide, the concentration of sulfuric acid, particle size, and solid-to-liquid ratio on sulfuric acid-hydrogen peroxide leaching were investigated. The results show that the optimal leaching conditions were leaching time of 120 min, the temperature of 60 °C, H 2 O 2 dosage of 1 mL/g, H 2 SO 4 concentration of 200 g/L, particle size of 200 mesh, and solid-to- liquid ratio of 1:4. Leaching rates for As and Cu were 98.42% and 97.57%, with As and Cu concentrations of 38.2 and 3.73 g/L in the leaching solution, respectively. During the reduction of As(V) using SO 2 in the leaching solution, the optimal conditions were SO 2 flow rate of 60 mL/min, reaction temperature of 10 °C, and reaction time of 2 h. The reduction efficiency of As(V) reached 95.75%, with the purity of As 2 O 3 achieving 98.71%. The overall recovery rate of As throughout the entire process was 90.67%.
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