Arsenic leaching

Arsenic leaches from the base of the ARS, transports through the underlying clayey soil, and into the underlying aquifer producing the high concentration in MW17. 

Insight into the oxidation process is given by Kim (1999) and Kim et al. (2000), who conducted leaching studies of H-15D core samples and found the amount of arsenic leached increases with the molar NuHCOb... 

The arsenic penetrates deeply into the wood and remains there for a long time. However, some of the chemical may migrate from treated wood into surrounding soil over time and may also be dislodged from the wood surface upon contact with skin. The amount and rate at which arsenic leaches, however, varies considerably depending on numerous factors, such as local climate, acidity of rain and soil, age of the wood product, and how much CCA was applied. Interestingly, the leaching occurs more with newer structures and decreases with time. 

One of the most tragic examples of water as a vector for toxic substances in the geosphere happened in Bangladesh, where tube wells drilled to supply pathogen-free water (Figure 9.9) became contaminated with arsenic leached from the aquifers into which they were drilled and caused numerous cases of arsenic poisoning. Characterized by the World Health Organization as... 

Wet Process. The sodium arsenate and stannate slag are treated by a leach and precipitation process to produce calcium arsenate, calcium stannate, and a sodium hydroxide solution for recycle. The sodium antimonate filtercake containing selenium, tellurium, and indium is treated in a special metals refinery to recover indium and tellurium. 

The cmde oxide is pressure-leached in a steam-heated autoclave using water or circulating mother hquor. The arsenic trioxide dissolves, leaving behind a residue containing a high concentration of heavy metal impurities and sihca. The solution is vacuum-cooled and the crystallisation is controUed so that a coarse oxide is obtained which is removed by centrifuging. The mother hquor is recycled. The oxide (at least 99% purity) is dried and packaged in a closed system. 

Dezincification As either plug dezincification (localized corrosion) or layer dezincification (general corrosion) and refers to zinc (Zn) being selectively leached out of brass. It can be prevented either by reducing the Zn content to below 15% or by the addition of trace amounts of inhibiting elements such as arsenic (As)... 

This hematite is not soluble in the cyanide solution. The oxidative pretreatment of gold ores thus reduces the cyanide consumption. Some impurity elements inhibit leaching reactions, examples include elements, carbon, sulfur and arsenic in gold ores are such impurities, but these can be removed by heating in air. 

Wastewater is generated in the primary zinc and primary cadmium recovery subcategories by acid plant blowdown, which results from sulfuric acid recovery, air pollution control, leaching, anode/ cathode washing, and contact cooling. The streams may contain significant concentrations of lead, arsenic, cadmium, and zinc. Tables 3.26 and 3.27 present classical and toxic pollutant data for the primary zinc and primary cadmium subcategories. 

KEYWORDS arsenic, contaminated aquifer, leaching, adsorbent surface, mineralogy... 

In the extraction procedure for sediments an initial leach with 6M hydrochloric acid was used in order to remove the bulk of carbonate and hydrated oxide phases before extraction with sodium hydroxide solution. This procedure gave a recovery of ca. 70% of the total arsenic in the sediment as determined following total decomposition. 

V. Dutre and C. Vandecasteele, Solidification/stabilization of arsenic-containing waste leach tests and behaviour of arsenic in the leachate. Waste Manage. 15 1 55-62, 1995. 

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