Arsenic Release from a Natural Rock under Near‐natural Oxidizing Conditions

Abstract

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 ...

Leaching behavior of arsenite and arsenate from the contaminated sediment by the effect of phosphate ion under anaerobic conditions

“…It is established that the most of these investigations have been based on to measure total arsenic from the various environmental samples (Rigol et al 2009;Noubactep et al 2008;Noubactep 2012;Igarashi et al 2008;Tabelin and Igarashi 2009). However, in the sequential extraction procedure (SEP) ammonium dihydrogen phosphate (NH 4 H 2 PO 4 ) has been used for arsenic leaching (Fedotov et al 2005;Lombi et al 2000) and finally total arsenic is measured without distinguishing arsenite and arsenate.…”

An Integrated Approach to Identify Water Resources for Human Consumption in an Area Affected by High Natural Arsenic Content

“…The results of leaching tests carried out on a VI rock sample and a CI rock sample, both with similar arsenic contents of about 30 mg/kg, show that the release of arsenic in steady state conditions is very small: the fractions of total bulk arsenic in the whole rock released from VI and CI samples are about 0.8% and 0.4%, respectively, after 168 h. The trends of release of the two samples are similar, as shown in Figure 10. The leaching tests were performed using deionized water as in other literature papers simulating water-rock or soil-water interactions [43][44][45]50,51] and also the effect of infiltration [52]. The use of real groundwater of the investigated area was not suitable, because its arsenic content (result of different factors including the natural rock-water interaction) would alter the study of the desorption/leaching behaviour we were investigating, as demonstrated by the results (not showed here) of preliminary tests performed for the choice of the experimental conditions.…”

Geochemical Implications of CO2 Leakage Associated with Geologic Storage: A Review

“…While the concept that lowering pH could enhance the dissolution of aquifer minerals and increase aqueous concentrations of contaminants in groundwater is reasonable, in the case of sulfides or other redox-sensitive minerals, redox conditions would be expected to have the greatest effect on their precipitation and dissolution behavior (Abdelouas et al 1999;Lee and Hering 2005;Rashid et al 2002;Sasaki et al 2010;Nickson et al 2000;Noubactep et al 2008;Smedley and Kinniburgh 2002;Edwards et al 2000). Thus, considering the influence of CO 2 intrusion rate on both pH and Eh and their coupled effects on the beneficial and deleterious reactions in the subsurface would provide a more complete scenario of what to expect within a particular environment.…”

“…Such effects further indicate that gas composition could have significant implications for the mobility of As and other redox-sensitive contaminants (e.g., V, U, Se and Cr) in the subsurface, since their mobility is strongly influenced by speciation (Abdelouas et al 1999;Lee and Hering 2005;Rashid et al 2002;Sasaki et al 2010;Nickson et al 2000;Noubactep et al 2008;Smedley and Kinniburgh 2002). In cases where gas composition favors a shift from more to less mobile species (e.g., As(III) or Cr(VI) to As(V) and Cr(III), respectively), CO 2 intrusion could be considered beneficial, while in cases where the alternative shift is favored, then CO 2 intrusion would be deleterious.…”

“…For example, many groundwater contaminants are redox-sensitive, or contained in redox-sensitive minerals Edmunds et al 1989). It is the dissolution and precipitation of these minerals that will drive the total aqueous concentrations of redox-sensitive contaminants (Abdelouas et al 1999;Lee and Hering 2005;Rashid et al 2002;Sasaki et al 2010;Nickson et al 2000;Noubactep et al 2008;Smedley and Kinniburgh 2002). Therefore, laboratory studies involving aquifer sediments and seeking to assess how CO 2 intrusion would impact the geochemistry of the aquifer should be conducted under redox and solution conditions relevant to that system.…”