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This paper describes the effects of pH, dissolved oxygen (DO), redox conditions, and mixing ratio of different rocks on the leaching behaviors of As and Pb from hydrothermally altered rock as well as the functional groups incorporating As and Pb in the rock. Most of As and Pb were incorporated in the residual or crystalline phase although significant amounts were also determined to be exchangeable, with carbonates and with FeMn oxides. Under oxic conditions, As and Pb showed similar leaching behaviors at similar pH values, a higher mobilization in the acidic and alkaline regions and a minimum at circumneutral pH. The absence of DO restricted the oxidation of sulfide minerals that also contained significant quantities of As resulting in a lower As release under these conditions. Strongly reducing conditions favored the release of As by the reductive dissolution of FeMn oxides and prevention of carbonate precipitation while the same conditions immobilized Pb because of its re-precipitation under reducing conditions. In general, depending on the pH, DO, and redox conditions, the major modes of As and Pb release from these sources could be either one or more of the following mechanisms: acid dissolution, reductive dissolution, ion exchange, desorption and sulfide oxidation processes.

The authors report on a microneedle-based amperometric nonenzymatic glucose sensor for painless and continuous monitoring of glucose. It consists of 3 × 5 sharp stainless steel microneedles micromachined from a stainless steel substrate. The microneedles are 600 and 100 μm in height and width, respectively. Nafion and platinum black were sequentially coated onto the tip of gold-coated microneedles and used for nonenzymatic (direct) sensing of glucose. Attractive features of the modified microneedle electrode include (a) a low working potential (+0.12 V vs. Ag/AgCl), (b) a linear response in the physiologically relevant range (1-40 mM), (c) a sensitivity as high as 175 μA mM cm, (d) a 23 μM detection limit, and (e) a response time of 2 s. The sensor also exhibits good reproducibility and stability. The sensor is selective for glucose even in the presence of 10-fold higher concentrations of ascorbic acid, lactic acid, dopamine, uric acid, and acetaminophen. Graphical abstract Schematic representation of the fabrication sequence for a nonenzymatic electrochemical glucose sensor using Nafion and platinum black coated microneedle electrode array. The sensor is based on measuring the faradaic current at +0.12 V vs. Ag/AgCl by the direct electrochemical oxidation of glucose to gluconic acid on the surface of a Pt black sensing layer.

This paper describes the mobilization and speciation of arsenic (As) found in hydrothermally altered rock under oxic column conditions. The altered rock sample was obtained from a tunnel project located in the Nakakoshi area of Hokkaido, Japan, whose geology is represented by slate, shale and sandstone. This area underwent silicification, pyritization and argillic alteration resulting in the As-enrichment of the rock.Results of the column experiments show that the infiltration rate, bulk density and rock bed thickness affected the duration of water residence, which in turn influenced the pH of the rock-water system. Coexisting ions most notably calcium (Ca 2+) at amounts greater than ca. 50 mg/L retarded the mobilization of As. Mobilization of As from the rock with time occurred in two stages: stage 1 (weeks 1 -20) with higher As leaching and stage 2 (weeks 20 -76) characterized by nearly constant As release. In addition, pore water As concentrations revealed that the columns developed into two regions: the top half where most of the leaching occurred and the bottom part dominated by adsorption. Thus, the mechanisms controlling the mobilization of As from the rock is a combination of one or more of the following processes: dissolution of soluble As-bearing fractions, pyrite oxidation and adsorption reactions. Arsenite (As [III]) was the dominant species in the effluent at the start of the experiment in columns with shorter water residence time and lower pH conditions (< 8). On the other hand, arsenate (As[V]) was the major inorganic species released from the rock at higher pH (8 -9.5) and when the system was close to equilibrium. Speciation of As with depth also indicated that As[III] disappeared around the bottom half of the columns, probably as a result of adsorption and/or oxidation. Arsenic speciation is partially controlled by the pH dependent adsorption of As species. The important adsorbent phases in the rock included Fe-Al oxides/oxyhydroxides, clay minerals and organic matter, which permitted the columns to attenuate additional As loadings including As [III]. Implications of these results on the design of a novel disposal method for these altered rocks include the enhancement of As adsorption through the addition of natural or artificial adsorbents and the utilization of a covering soil with low permeability to minimize rainwater infiltration into the rock.

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The continuous accumulation of artisanal and small-scale gold mining (ASGM) tailings in the Philippines without adequate storage and disposal facility could lead to human health and environmental disasters in the long run. In this study, ASGM tailings was simultaneously stabilized and repurposed as construction material via geopolymerization using coal fly ash, palm oil fuel ash and a powder-based alkali activator. Scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS) identified iron sulfides in the tailings containing arsenic (As), cadmium (Cd), copper (Cu), lead (Pb) and zinc (Zn), which could be released via weathering. The average unconfined compressive strengths (UCS) of tailings-based geopolymers at 14 days curing were 7.58 MPa and 7.7 MPa with fly ash and palm oil fuel ash, respectively. The tailings-based geopolymers with palm oil fuel ash had higher UCS most likely due to CASH reaction product formation that improved strength formation. The toxicity characteristic leaching procedure (TCLP) results showed very low leachabilities of As, Pb and Fe in the geopolymer materials suggesting ASGM tailings was effectively encapsulated within the geopolymer matrix. Overall, the geopolymerization of ASGM tailings is a viable and promising solution to simultaneously stabilize mining and industrial wastes and repurpose them into construction materials.

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