Reductive roasting of arsenic-contaminated red mud for Fe resources recovery driven by johnbaumite-based arsenic thermostabilization strategy.

Arsenic-contaminated red mud (As-RM) is a hazardous waste with limited recycling approaches. Generally, through reductive roasting and magnetic separation, RM could be transformed into Fe-rich concentrate for Fe resource recovery. However, due to the poor thermostabilization of As species, reductive roasting of As-RM would cause severe As volatilization pollution together with high As leaching risks from heated residue. Herein, a novel johnbaumite-based As thermostabilization strategy is developed for clean Fe resources recycling from As-RM. We found that in the presence of Ca(OH)2, the As species in As-RM could be immobilized as thermostable and insoluble johnbaumite (Ca5(AsO4)3OH) at 900 °C, effectively enhancing the As thermostability and insolubility. Introducing 1.5% Ca(OH)2 into As-RM suppressed the As volatilization ratio from 60.3% to 15.7% during reductive roasting. Meanwhile, the As leaching concentration of the reduced residue was reduced to < 100 µg/L, thus satisfying the Japanese wastewater discharge standard. A concentrate with approximately 67.5% total iron grade was obtained from As-RM through this clean reductive roasting and magnetic separation. Overall, the approach introduced in this work effectively reduces the As diffusion pollution deriving from As-RM thermal reduction, which could contribute to hazardous As-RM reutilization, clean Fe resources recovery, and As pollution mitigation.

Antimicrobial Activity of Polysorbate 80-iodine Complex: Polysorbate 80 Firmly Retains Iodine.

Considering that iodine is highly volatile and has low solubility in water, it is utilized as an antiseptic in its complex form (iodophor) with a carrier material. Herein, we prepared the polysorbate 80-iodine complex and investigated its properties. In the presence of 0%, 0.01%, 0.1%, and 1% polysorbate, Pseudomonas putida NBRC 100650 growth was inhibited at 75, 75, 50, and 25 ppm iodine, respectively, indicating that high concentrations of polysorbate 80 enhanced the antibacterial activity of iodine. Absorption spectra of the mixtures of polysorbate 80 and iodine were analyzed; we observed that two peaks at 287 and 350 nm, derived from triiodide ions, shifted to the longer wavelength side in the presence of 0.1% and 1% polysorbate 80. Further, when 1% polysorbate 80 was added to the mixture of soluble starch and iodine, the peak around 580 nm arising from the amylose-iodine complex disappeared, indicating that polysorbate 80 captured iodine from the starch-iodine complex. We also found that polysorbate 80 retained iodine for approximately 4 months and prevented its volatilization; moreover, the mixture did not lose its growth inhibitory activity upon storage for approximately 4 months. Collectively, our data indicated that polysorbate 80 firmly retains low concentrations of iodine and that the polysorbate 80-iodine complex can serve as an antiseptic that can be stably stored for a long time.

Protonation stabilized high As/F mobility red mud for Pb/As polluted soil remediation.

The hazardous red mud (RM) with high As/F mobility and heavy metal contaminated soil have constituted severe environmental threats. This work demonstrates a "waste to eco-material" strategy through a reliable and low-cost protonation approach to eliminate the As/F leaching risk of RM, and then recycle it as heavy metal passivators for Pb/As polluted soil remediation. The As/F anions have been immobilized by the protonated Fe/Al (hydr)oxides within RM via the formation of stable As/F compounds during the protonation process, which satisfies the requirement by the World Health Organization (As leaching <0.01 mg/L; F leaching <0.8 mg/L). Moreover, in the oilseed rape pot experiments, by adding 30 g/kg stabilized RM into Pb/As polluted soils (100 ~ 300 ppm), benefited from its large adsorption capacity, approximately 40.9 ~ 49.7% Pb and 40.8 ~ 54.8% As concentrations in the plant are reduced without adverse effects. The whole process for RM treatment and soil remediation is cost-effective, straightforward and eco-friendly without secondary pollution or soil degradation. This research provides a green chemical strategy to address both RM recycling and heavy metal contaminated soil remediation problems, which shows high economic feasibility and ecological benefits.

Reclamation of an arsenic-bearing gypsum via acid washing and CaO-As stabilization involving svabite formation in thermal treatment.

As one of the biggest hazardous solid waste in the metallurgical industry, arsenic-bearing gypsum (ABG) is a great threat to environmental safety owing to possible leakage and diffusion contamination. However, the reclamation of ABG suffers great challenges due to its worthless constituents and high arsenic leaching. In this study, an ABG was reclaimed as more valuable bassanite (CaSO4∙0.5H2O) and anhydrite (CaSO4). Firstly, the overmuch arsenic in ABG was removed to below 150 mg/kg (Japan standard value) using acid extraction. Then, the sludge was mixed with a small amount of CaO and heated at 150 °C and 900 °C to produce bassanite and anhydrite, respectively. In this calcination, gypsum dehydration and arsenic stabilization were combined. In Japan standard leaching test (JSLT), the arsenic leaching concentrations from bassanite (5.1 µg/L) and anhydrite (1.3 µg/L) satisfied the environmental criteria (<10 µg/L) set by Japan government and remained stable for three months. In toxicity characteristic leaching procedure (TCLP), arsenic leaching concentrations remained at 1.61 and 0.61 mg/L, much lower than the limitation (<5 mg/L). Moreover, the arsenic leaching behavior implied that higher temperature was benefited to arsenic stability, which indicated that the arsenic stabilization process was temperature dependent. By XRD analyses, it was found that heating (over 100 °C) could effectively promote arsenic immobilization through reducing the carbonation influence. And the temperature dependence was attributed to the formation of insoluble svabite (Ca5(AsO4)3OH) at high temperature (300-900 °C).

Removal of boron from wastewater by the hydroxyapatite formation reaction using acceleration effect of ammonia.

The mechanism was discussed for the removal of boron by the hydroxyapatite (HAp) formation reaction using Ca(OH)(2) and (NH(4))(2)HPO(4) in room temperature. Time required to remove boron was 20 min by adding Ca(OH)(2) and (NH(4))(2)HPO(4) for the remaining boron to below 1mg/L. The removal rate of boron was controlled by the HAp precipitate formation and the presence of ammonia. From the XRD patterns and SEM images, HAp could be confirmed in the precipitate product. The reaction between borate ions and calcium hydroxide was accelerated by dehydration with ammonia; the borate-calcium hydroxide compound coprecipitated with resulting HAp. Although the removal of boron decreased in the presence of sulfate, phosphate, and aluminum, these effects could be prevented by adding excess Ca(OH)(2). Interference of fluoride ions was eliminated by adding Al(3+). Sodium alpha-olefin sulfonate was the most effective coagulant for HAp precipitation. The proposed boron removal method has several advantages about treating time and ability of boron removal. The method was successfully applied to the real hot spring wastewater.

Visual colorimetry for trace antimony(V) by ion-pair solid-phase extraction with bis[2-(5-chloro-2-pyridylazo)-5-diethylaminophenolato]cobalt(III) on a PTFE type membrane filter.

A new visual colorimetry for trace antimony(V) based on ion-pair solid-phase extraction to a PTFE-type membrane filter with bis[2-(5-chloro-2-pyridylazo)-5-diethylaminophenolato]cobalt(III) ion ([Co(5-Cl-PADAP)(2)](+)) has been developed. Experiments showed that hexachloroantimonate(V) ion (SbCl(6)(-)) was adsorbed with [Co(5-Cl-PADAP)(2)](+) to the front surface of the PTFE filter. The adsorption of antimony(V) ion was promoted by the addition of lithium chloride as a source of chloride ion. The excess reagent of [Co(5-Cl-PADAP)(2)](+) was eluted by rinsing with a 10 wt% methanol aqueous solution. In this case, the slow rate of the hydrolysis reaction of SbCl(6)(-) and the difference of the hydrophobicity of the ion pairs were important for adsorption and separation with a PTFE-type membrane filter. The antimony(V) concentration was determined through a visual comparison with a standard series. The visual detection limit was 0.10 microg. The calibration curve assessed with the reflection spectrometric responses at 580 nm was linear in the concentration range of 0.10 - 1.2 microg (r = 0.996). The proposed method has been applied to the determination of sub-microgram levels of antimony(V) ion in water samples.

Tristimulus colorimetry using a digital still camera and its application to determination of iron and residual chlorine in water samples.

Tristimulus colorimetry using a digital still camera (DSC) as a colorimeter has been developed. A photograph of a sample and standard solutions was taken simultaneously with the DSC, and it was transferred to a PC. On the PC, the colors of the sample and of the standard solutions were analyzed and L* (brightness), a* (red-green component), and b* (yellow-blue component) values were determined with laboratory-made software. A dedicated light-box containing white-color LEDs as light source was made of white acrylic to make constant exposure at each photograph. Various settings of the DSC, such as exposure mode, white balance, and so on, that affect analytical figures, were studied with determination of iron with 1,10-phenanthroline. This method was successfully applied to the determinations of iron in a river water sample and of residual chlorine in tap water samples with N,N-diethylphenylenediamine (DPD).