Arsenate

This paper aims at a full description of the Raman and Infrared spectra of the arsenate mineral tilasite, CaMg(AsO4)F, from Långban, Värmland, Sweden. X-ray diffraction showed the two samples to be phase pure with a monoclinic unit cell of a = 6.683(3) Å, b = 8.950(5) Å, c = 7.572(4) Å, and β = 121.09(2)°. The infrared and Raman spectra were dominated by the arsenate modes. The two highest intensity bands were observed at 850 cm–1 and 831 cm–1 and were assigned to the Raman active ν1 symmetric stretching vibration (A1) and the Raman active triply degenerate ν3 antisymmetric stretching vibration (F2). The Raman and infrared active triply degenerate ν3 antisymmetric stretching vibration (F2) was observed in the infrared spectrum at 822 cm–1, 792 cm–1, and 761 cm–1. The intense Raman band at 465 cm–1 was assigned to the Raman active triply degenerate ν4 bending vibration (F2). The corresponding infrared bands were observed at 523 cm–1, 449 cm–1, and 414 cm–1. The intense Raman band at 329 cm–1 was attributed to the Raman active doubly degenerate ν2 symmetric bending vibration (E). Lowering of the symmetry of the tetrahedral arsenate group led to significant splitting of these modes. The low wavenumber region below 320 cm–1 was assigned to metal-oxygen stretching and lattice vibrations.  In the range of 1000–1100 cm–1, four very weak bands were observed. These bands were probably due to the ν3(F2) of a very small amount of phosphate substituted for arsenate in the crystal structure of tilasite.

Drinking water contaminated with arsenic above permissible limit imposes major health issues on mankind due to its carcinogenic nature. Some of the conventional treatment methods like adsorption assisted with oxidation or membrane processes/reverse osmosis proved to be effective options. Few obstacles such as high capita cost and dif icult handling ofreject water or used media made groundsfor having a discussion over these technologies. Integrated approach using two or more technologies together helps in getting effective results. Membrane distillation process combined with reverse osmosis, ion exchange or nano-filtration and synthesis of nanoparticles are some of the innovative measures taken so far. This review aims to comprehensively discuss conventional as well as advanced removal techniques and compare their performances. Special focus has been made while discussing potential of nanoparticles of metal oxides as adsorbents.

... Adsorption of Arsenic on Layered Double Hydroxides: Effect of the Particle Size. Li Yang, Megha Dadwhal, Zoya Shahrivari, Mayur Ostwal, Paul KT Liu, Muhammad Sahimi, and Theodore T. Tsotsis. Industrial & Engineering Chemistry Research 2006 45 (13), 4742-4751. ...

The Raman spectrum of tyrolite, CaCu5(AsO4)2(CO3)(OH) 4·6H2O, from Brixlegg, Tyrol, Austria, is reported. Comparison with copper hydroxy–arsenate and basic carbonates was used to achieve assignments of the observed bands. The AsO43– group is characterized by two v4 modes around 433 and 480 cm−1 plus a broad band around 840 cm−1 as the v3 overlapping with the v1. The v2 mode is observed as a single band around 355 cm−1. The CO32–v1 mode is observed around 1035 and 1088 cm−1, although this assignment is difficult because of the in-plane OH bending vibrations at similar frequencies. Two v4 modes are assigned to the 717 and 755 cm−1 bands. The v3 mode is present as three bands at 1431, 1463, and 1498 cm−1. A large split caused by bridging carbonates may explain the band at 1370 cm−1. The H2O bending region shows two bands at 1635 and 1667 cm−1 together with stretching modes around 3204 and 3303 cm−1, the first associated with adsorbed H2O, while the second indicates more strongly bonded H2O. Three bands around 3534, 3438, and 3379 cm−1 are assigned to OH stretching modes of the OH groups in the crystal structure. The 202, 262, 301, 524, and 534 cm−1 bands are assigned to Cu–OH bending and stretching modes, whereas the bands around 179, 202, and 217 cm−1 are ascribed to O–(Ca, Cu)–O(H) with the O(H) at much greater distance from the cation. The bands around 503, 570, and 598 cm−1 are ascribed to the Cu–O stretching modes.

Abstract Inorganic arsenic (As) speciation and behaviour were studied in the Gironde Estuary, a major European estuary in the south west of France. For the first time ever, the dynamic (potentially bioavailable) fraction of inorganic arsenite, As(III), and arsenate, As(V), were quantified in this estuary, using an antifouling gel-integrated gold microelectrode interrogated by square wave anodic stripping voltammetry (GIME-SWASV). The concentrations of dissolved As(III) and As(V) were determined by hydrid generation-flow injection-atomic absorption spectrometry (HG-FI-AAS) and inductively coupled plasma-mass spectrometry (ICP-MS) in collected samples following filtration through 0.2 μm, as well as 0.02 μm pore size filters. The concentrations of arsenite in the dynamic fraction, As(III)dyn, ranged from 1.3 to 3.3 nM, contributing almost completely to the dissolved arsenite, As(III)diss, which ranged between 0.9 and 3.1 nM in the 0.2 μm fraction, and between 1.2 and 3.7 nM in the 0.02 μm fraction. Concentrations of arsenate in the dynamic fraction, As(V)dyn, ranged from 0.9 to 22.9 nM, and contributed to the dissolved arsenate, As(V)diss, by 4–73% in the 0.2 μM fraction, and by 5–90% in the 0.02 μm fraction. The concentrations of As(V)diss in the 0.2 μm fraction were between 14.5 and 36.2 nM, and between 15.2 and 34.9 nM in the 0.02 μm fraction. The impact of this work is two-fold. Measurements of As species with different techniques allowed one to validate the on-board GIME voltammetric measurements. In addition, determination of As species in different fractions, as well as combining the obtained results with the conducted measurements of dissolved Mn and Fe, particulate suspended matters, and master physicochemical parameters (T, pH, O2, redox E), helped to broaden the understanding of biotic and abiotic processes governing the distribution of arsenic, especially its potentially bioavailable forms, in the Gironde Estuary.