Review of various treatment technologies for arsenic in inorganic solids

2 Review of various treatment technologies for arsenic in inorganic solids 7.3.2.1 Site isolation 

In situ solidification/stabilization refers to the injection and mixing of binders into contaminated soils and sediments. Although the process can be effective, obstructions, deep contamination, shallow water tables, 

Rachakomkij, 2007, 602-603). The released As(V) then reacted with calcium to form calcium arsenates. As previously mentioned, the long-term stability of calcium arsenates depends on ambient conditions. In the presence of carbon dioxide from air or carbonate in water, calcium arsenates may decompose over time and release arsenic (Robins and Tozawa, 1982 Ghimire el al., 2003, 4946 Jing, Korfiatis and Meng, 2003, 5055-5056). 

Shih and Lin (2003) investigated the solidification/stabilization of arsenic-rich flyash from an abandoned copper smelter in northern Taiwan. The flyashes (2-40 % total arsenic, mostly as As(III)) were collected from three flue gas discharge tunnels. Extremely high cement dosages (cement/waste mass ratio of greater than 6) were required to stabilize the wastes so that they would pass the US TCLP for arsenic ( 5 mg L 1 Appendix E). (The TCLP is often used in research outside of the United States.) Cement dosages could be reduced and the mixtures would still pass the TCLP for both arsenic and lead if municipal waste incinerator flyash was added. Lime alone was able to stabilize arsenic and pass the TCLP however, the leachates exceeded the TCLP lead standard of 5mgL 1. The immobilization of arsenic in lime may be due to the formation of sparsely water-soluble calcium arsenites and arsenates, such as CaHAsC 3 //1LO or Ca3(AsC 4)2 H20, where n 0 (Shih and Lin, 2003, 692). 

Kahakachchi, Uden and Tyson (2004) investigated the ability of various liquids to extract As(III), As(V), DMA(V), and MMA(V) from spiked soils. The extractants included deionized water, a citrate buffer, an ammonium dihydrogen phosphate buffer, 1M phosphoric acid, 5 % acetic acid, household vinegar, 0.1 M NaOH, and even Coca Cola . After eight days, the highest extractions for As(III), MMA(V), and As(V) were achieved with NaOH at 46, 100, and 84%, respectively. A 10 mM citrate buffer was most effective with DMA(V) with about 85 % removal after eight days. 

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