The sorption of Np(V) to synthetic hydroxyapatite was determined in batch experiments in a 0.1M NaClO

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It was discovered that MgO or Mg(OH)* when it reacts with water is a very strong sorbent for arsenic. Distribution constants, or & values, are as high as 1 x lo6 Umole. In this work, Mg(0H)z and other compounds have been investigated as sorbents for arsenic and other contaminants. This work has resulted in several major accomplishments including: 1) design, construction, and testing of a pressure sand filter to remove Mg(0H)z after it has sorbed arsenic from water, 2) stabilization of Mg(OH)2 as a Sorrel's cement against reaction with carbonate that results in MgC03 formation decreasing the efficiency of Mg(OH)2 to sorb arsenic, and 3) the development of a new, very promising sorbent for arsenic based on zirconium. Zirconium is an environmentally benign material found in many common products such as toothpaste. It is currently used in water treatment and is very inexpensive. In this work, zirconium has been bonded to activated carbon, zeolites, sand and montmorillonite. Because of its high charge in ionic form (+6), zirconium is a strong sorbent for many anions including arsenic. In equilibrium experiments arsenic concentrations in water were reduced from 200 ppb to less than 1 ppb in less than 1 minute of contact time. Additionally, analytical methods for detecting arsenic in water have also been investigated. Various analytical techniques including HPLC, AA and ICP-MS are used for quantification of arsenic. Due to large matrix interferences HPLC and AA techniques are not very selective and are time consuming. ICP-MS is highly efficient, requires a low sample volume and has a high tolerance for interferences. All these techniques are costly and require trained staff, and with the exception of ICP-MS, these methods cannot be used at low ppb arsenic concentration without using a pre-concentration step. An alternative to these traditional techniques is to use a colorimetric method based on leucocrystal violet dye interaction with iodine. This method has been adapted in our facility for quantifying arsenic concentrations down to 14 ppb.

Two sorbents, zirconium coated zeolite and magnesium hydroxide, were tested for their effectiveness in removing arsenic from Albuquerque municipal water. Results for the zirconium coated zeolite indicate that phosphate present in the water interfered with the sorption of arsenic. Additionally, there was a large quantity of iron and copper present in the water, corrosion products from the piping system, which may have interfered with the uptake of arsenic by the sorbent.