11The solubilization of arsenic (As) from an ore material (native Arsenic [As, trig.] with 12Lollingite [FeAs 2 , rh.]) was characterized in leaching tests lasting for ≤ 99 days. The 13 experiments were performed with materials of different particle sizes (≤ 2 mm), in different 14 waters and under test conditions relevant to As mobilization at near surface contaminated 15 sites. The impact of dolomite [CaMg(CO 3 ) 2 ], metallic iron (Fe 0 ), and pyrite (FeS 2 ) on As 16 release was accessed. Two different types of batch experiments were conducted with a 17 constant amount of the base material and different types of water (deionised, mineral, spring, 18 and tap water). For comparison parallel experiments were conducted with 0.1M EDTA, 0.1M 19 Na 2 CO 3 and 0.1M H 2 SO 4 . The results indicated no significant effect of carbonate addition on 20As solubilization. Fe 0 and FeS 2 addition essentially slowed the initial As solubilization. 21 H 2 SO 4 was the sole leaching agent significantly influencing As solubilization from the base 22 material. The general trend assuming that "the smaller the particle size the quicker the As 23 release" was not strictly verified because in samples of smaller particle sizes (d < 0.063) As 24 was partly oxidized to more stable species. 25Key Words: Carbonate, Native arsenic, Solubilization 26 27 2 Introduction 28The presence of arsenic (As) in many minerals, mining wastes, industrial wastewater and 29 waterways is a serious pollution problem [1][2][3][4]. The treatment of such contaminated materials 30 by conventional techniques is often expensive. A recent development to remediate such a 31 contamination is the implementation of permeable reactive barriers [5][6][7][8][9][10]. Most of the 32 current full-scale reactive barriers use metallic iron (Fe 0 -based alloys widely termed as 33 zerovalent iron) as treatment medium. An iron reactive barrier can be placed immediately 34 down gradient of the contaminant source (e.g. mining wastes) to prevent a plume from 35 developing. Arsenic is leached from mining wastes by infiltrating surface water or flowing 36 groundwater to the reactive barrier. Therefore, to properly design a treatment wall, it is 37 essential to characterize the leaching behaviour of natural waters for contaminant source 38 materials (natural ores, mining wastes). The bicarbonate (HCO 3 -) content of subsurface waters 39 has been controversially discussed in the literature as possible important parameter 40 controlling their As mobilization capacity as discussed below. 41In the last decades substantial efforts were made to elucidate the origin of As in contaminated 42 groundwaters [1,[11][12][13][14][15][16][17][18][19][20][21][22]. The univocal result of these efforts is that As mostly originates from 43 natural background sources. However, the individual processes leading to As release and their 44 relative importance are yet to be fully elucidated [16,[23][24][25][26][27][28]. There are three main theories 45 concerning As release into the environment ...
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