Development of an automated technique for the speciation of arsenic using flow injection hydride generation atomic absorption spectrometry (FI-HG-AAS)

Adsorption of arsenic species from water using activated siderite-hematite column filters

Arsenic is present at relatively high concentrations in surface water and groundwater as a result of both natural impacts and anthropogenic discharge, which requires proper treatment before use. The present study describes As adsorption on a siderite-hematite filter as a function of activating condition, empty bed contact time, and As species. Hydrogen peroxide activating increased As adsorption on siderite by 16.2 microg/g, and on hematite by 13.0 microg/g. The H2O2 conditioning enhanced adsorption efficiency of activated siderite-hematite filters up to throughput of 500 pore volumes of 500 microg/L As water. At values greater than 47 min, the empty bed contact time (EBCT) had only a weak influence on the removal capacity of pristine siderite-hematite filters. Due to the formation of fresh Fe(III)-oxide layer in the H2O2-conditioned filter and the pristine hematite-siderite filter, both of them may be utilized as a cost-effective reactor for treating As water. A toxicity characteristic leaching procedure (TCLP) test showed that the spent minerals were not hazardous and could be safely landfilled.

Adsorption of arsenic(III) and arsenic(V) from groundwater using natural siderite as the adsorbent

Batch and column tests were performed utilizing natural siderite to remove As(V) and As(III) from water. One hundred milligrams of siderite was reacted at room temperature for up to 8 days with 50 mL of 1000 microg/L As(V) or As(III) in 0.01 M NaCl. Arsenic concentration decreased exponentially with time, and pseudoequilibrium was attained in 3 days. The estimated adsorption capacities were 520 and 1040 microg/g for As(V) and As(III), respectively. Column studies show that effluent As was below 1.0 microg/L after a throughput of 26,000 pore volumes of 500 microg/L As water, corresponding to about 2000 microg/g of As load in the filter. Results of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) reveal that high As retention capacity of the filter arose from coprecipitation of Fe oxides with As and subsequent adsorption of As on the fresh Fe oxides/hydroxides. Arsenic adsorption in the filter from As-spiked tap water was relatively lower than that from artificial As solution because high HCO(-)(3) concentration restrained siderite dissolution and thus suppressed production of the fresh Fe oxides on the siderite grains. The TCLP (toxicity characteristic leaching procedure) results suggest that these spent adsorbents were inert and could be landfilled.

Mechanism of volatile hydride formation and their atomization in hydride generation atomic absorption spectrometry

The mechanism of volatile hydride generation (HG) and the formation of analyte atoms in the quartz cell atomizer used in the determination of hydride-forming elements (As, Bi, Ge, Pb, Sb, Sn, Te etc.) by atomic absorption spectrometry (AAS), have been critically reviewed. The nascent hydrogen mechanism failed to explain hydride generation under different experimental conditions when tetrahydroborate (THB), amineboreanes (AB) and cyanotrihydroborate (CBH) were used as reductants. Various experimental evidence suggested a non-nascent hydrogen mechanism, in which the transfer of hydrogen directly bonded to boron to an analyte takes place. In electrochemical hydride generation (EcHG), the reduction of the analyte species and subsequent hydrogenation was proposed. The mechanism of analyte atom formation in a quartz tube atomizer has been explained by the following hypotheses: thermal decomposition, oxidation by 02 and collisions by hydrogen free radicals. The free-radical mechanism satisfactorily explains most of the analytical implications. The significant variation in the experimental conditions required to generate different analyte hydrides makes it difficult to arrive at a generalized mechanism of hydride formation.