Immobilization of selenium by Mg-bearing minerals and its implications for selenium removal from contaminated water and wastewater

This study examines the possible immobilization of Se(VI) by Mg-bearing hydrotalcite and serpentine-like minerals. Selenate immobilization was carried out via adsorption and coprecipitation reactions under alkaline conditions. The effects of Mg/Al ratios, temperature and initial Se concentration on the adsorption and/or coprecipitation of Se6+ onto these Mg-bearing minerals were examined. The sorption mechanism of Se(VI) was examined by XAFS analysis to give account of its local coordination environment. The results showed that Se(VI) sorption behavior by hydrotalcite and serpentine-like minerals was mainly influenced by their Mg/Al ratio. Higher removal efficiency of Se(VI) (> 60 and 90% at 100 and 10 ppm initial Se concentration) was observed during coprecipitation onto hydrotalcite and serpentine-like phases with Mg/Al ratios of 2 and 1.25, respectively. The formation of Mg-bearing minerals was enhanced at higher temperature (at 75 degrees C) but the effect of temperature in Se(VI) immobilization was very minimal. Selenate was mainly retained via outer-sphere complexation but an irreversible fraction of sorbed selenate (about 20%) was observed in these mineral phases. In overall, this study has several important implications in the possible application of hydrotalcite and aluminian serpentine in Se(VI) immobilization

Adsorption and co-precipitation behavior of arsenate, chromate, selenate and boric acid with synthetic allophane-like materials

Pollution caused by boric acid and toxic anions such as As(V), Cr(VI) and Se(VI) is hazardous to human health and environment. The sorption characteristics of these environmentally significant ionic species on allophane-like nanoparticles was investigated in order to determine whether allophane can reduce their mobility in the subsurface environment at circum-neutral pH condition. Solutions containing 100 or 150 mmol of AlCl3. 6H2O were mixed to 100 mmol of Na4SiO4 and the pH were adjusted to 6.4 ± 0.3. The mineral suspensions were shaken for 1 hr and incubated at 80℃ for 5 days. Appropriate amounts of As, B, Cr and Se solutions were added separately during and after allophane precipitation. The results showed that As(V) and boric acid can be irreversibly fixed during co-precipitation in addition to surface adsorption. However, Cr(VI) and Se(VI) retention during and after allophane precipitation is mainly controlled by surface adsorption. The structurally fixed As(V) and boric acid were more resistant to release than those bound on the surface. The sorption characteristics of oxyanions and boric acid was also influenced by the final Si/Al molar ratio of allophane in which Al-rich allophane tend to have higher uptake capacity. The overall results of this study have demonstrated the role of allophane-like nanoparticles and the effect of its Si/Al ratio on As, B, Cr and Se transport processes in the subsurface environment

Removal of Cr from synthetic wastewater by sorption into volcanic ash soil

The possibility of using volcanic ash soils (VAS) or Andisols as a low-cost and natural adsorbent is investigated in this study for the removal of Cr (VI) from synthetic wastewater. Andisols can be used as adsorbent because they are characterized by the presence of non-crystalline secondary minerals such as allophane and imogolite that show variable charge characteristics and have the ability to retain cations and anions. The adsorption of Cr on to two VAS from Mt. Isarog and Mandalagan (B-Horizon), Philippines, was carried out at ambient temperature using batch adsorption studies. The effects of different parameters such as amount of adsorbent, contact time, initial Cr concentration and pH of the solution were investigated. The results showed that the VAS from Isarog is more effective in the removal of Cr than in Mandalagan. The maximum removal efficiency of the Isarog soil for a Cr concentration of 10 mg/L reached 89% with a dose of 20 g/L at a moderately acidic pH of 3. The Mandalagan soil on the other hand could remove only 65% at the same pH conditions and parameters. The difference in the removal of the two soils may be attributed to their physico-chemical properties in which the Isarog soil has higher clay content, porosity and lower bulk density. Isarog soil has fine particles with higher surface area and more active noncrystalline minerals and thus has higher removal efficiency than Mandalagan soil. Based on the results, the use of VAS from Isarog appears to be economical and an alternative to commercially available adsorbents for the removal of Cr from contaminated wastewater

Solid-phase partitioning of mercury in artisanal gold mine tailings from selected key areas in Mindanao, Philippines, and its implications for mercury detoxification

The solid-phase partitioning of mercury could provide necessary data in the identification of remediation techniques in contaminated artisanal gold mine tailings. This study was conducted to determine the total mercury content of mine wastes and identify its solid-phase partitioning through selective sequential extraction coupled with cold vapour atomic absorption spectroscopy. Samples from mine tailings and the carbon-in-pulp (CIP) process were obtained from selected key areas in Mindanao, Philippines. The results showed that mercury use is still prevalent among small-scale gold miners in the Philippines. Tailings after ball mill-gravity concentration (W-BM and Li-BM samples) from Mt Diwata and Libona contained high levels of mercury amounting to 25.024 and 6.5 mg kg(-1), respectively. The most prevalent form of mercury in the mine tailings was elemental/amalgamated mercury, followed by water soluble, exchangeable, organic and strongly bound phases, respectively. In contrast, mercury content of carbon-in-pulp residues were significantly lower at only 0.3 and 0.06 mg kg(-1) for P-CIP (Del Pilar) and W-CIP (Mt Diwata), respectively. The bulk of mercury in P-CIP samples was partitioned in residual fraction while in W-CIP samples, water soluble mercury predominated. Overall, this study has several important implications with regards to mercury detoxification of contaminated mine tailings from Mindanao, Philippines

Potential utilization of artisanal gold-mine tailings as geopolymeric source material: preliminary investigation

© 2018, Springer Nature Switzerland AG. In this study, chemical and mineralogical characterizations of gold-mine tailings in key mining areas in Mindanao, Philippines were investigated for possible utilization as geopolymeric source material. Results of X-ray fluorescence (XRF) and energy dispersive X-ray spectroscopy (EDS) showed that the mine tailings samples have significant amounts of silicon, aluminum and calcium, which are crucial elements needed for geopolymerization. This was confirmed by the IR spectroscopic and mineralogical characteristics of the tailings where vibration bonds and minerals associated with Al and Si such as kaolinite and zeolite are detected. These minerals are already established as indicators for a material to be a good feedstock for geopolymerization. Furthermore, one of the tailings samples had an Si/Al ratio of 4.81, which was close to the recommended value of 3.0 for geopolymerization. The compressive strength of the synthesized geopolymer bricks gained an average of 5.48 MPa. The results suggested that gold mine tailings from key mining areas in Mindanao, Philippines could be used as geopolymer source material

Annotated list of tiger beetles (Coleoptera, Cicindelidae) in Calanasan, Apayao Province, Luzon, Philippines

The forests of Apayao Province are one of the remaining and relatively unexplored areas in the Philippines. With the aim to make Calanasan in Apayao province a UNESCO biosphere reserve as a mechanism in protecting its species, an expedition to document the biodiversity was conducted. This paper presents an annotated list of the 12 species of tiger beetles found in Calanasan. The beetles were mostly collected through opportunistic sampling. In Calanasan, 75% of the tiger beetle species collected are endemic, which shows the high value in preserving this area. Thus, the nomination of Calanasan as a UNESCO biosphere reserve is highly recommended