Mobilization and speciation of arsenic from hydrothermally altered rock containing calcite and pyrite under anoxic conditions

Abstract

The effects of water residence time and anoxic conditions on the mobilization and speciation of arsenic (As) in a calcite-and pyrite-bearing altered rock excavated during a road-tunnel project has been evaluated using batch and column laboratory experiments. Higher infiltration rates (i.e., shorter water residence times) enhanced the leaching of As due to the higher pH values of the effluents and more rapid transport of dissolved As through the columns. The concentration of As in the effluent also increased under anoxic conditions regardless of the water residence time.This enhanced leaching of As under anoxic conditions could be attributed to a significant pH increase and decreased Fe oxyhydroxides/oxides precipitation compared to similar experiments done under ambient conditions. Processes that controlled the evolution of pH and the temporal release mechanisms of As under anoxic conditions were identical to those previously observed under ambient conditions: the dissolution of soluble phases, pyrite oxidation, co-precipitation and/or adsorption/desorption reactions. Speciation of As in the column experiments could partly be attributed to the pH-dependent adsorption of As species onto Fe oxyhydroxides/oxides precipitates. Moreover, apparent equilibriums of the total As and arsenite (As[III]) concentrations were delayed under anoxic conditions in both batch and column experiments.

Synthesis and characterization of coal fly ash and palm oil fuel ash modified artisanal and small-scale gold mine (ASGM) tailings based geopolymer using sugar mill lime sludge as Ca-based activator

“…To make matters worse, many Au deposits mined by ASGM operations are formed under hydrothermal conditions, well-known ore-forming geological phenomena that concentrate Au and base metals like copper (Cu), lead (Pb) and zinc (Zn) in sulfide minerals like pyrite (FeS 2 ), chalcopyrite (CuFeS 2 ) and arsenopyrite (FeAsS) ( Park et al., 2018a ; Tabelin et al., 2012a , b ). Upon exposure to the environment, sulfide minerals are dissolved via a combination of chemical-electrochemical reactions that are promoted by microorganisms ( Li et al., 2019a , b ; Seng et al., 2019a , b ; Tabelin et al., 2017a , 2020b ), a process that generates acidic and highly contaminated leachates containing toxic metalloids like arsenic (As) and selenium (Se) ( Marove et al., 2020 ; Tabelin and Igarashi, 2009 ; Tabelin et al., 2012c , 2017b ; Tamoto et al., 2015 ) and hazardous heavy metals like Cu and Zn ( Igarashi et al., 2020 ; Senoro et al., 2020 ; Tabelin et al., 2013 ; Tatsuhara et al., 2012 ; Tomiyama et al., 2019 , 2020 ).…”

Scaling effects on arsenic release from excavated hydrothermally altered rocks in column experiments

“…If not handled appropriately, these rocks can undergo weathering and oxidization, resulting in the release of toxic elements that can contaminate the soil and groundwater. In search of a proper disposal method and a reuse approach, the leaching behaviors of toxic elements (e.g., arsenic, selenium, and lead) in excavated rocks, including their mechanisms of release and migration, have been widely studied by conducting batch, column, and in situ leaching experiments in recent years (Igarashi et al 2008 ; Kamata and Katoh 2019 ; Kato et al 2023 ; Li et al 2016 ; Tabelin and Igarashi 2009 ; Tabelin et al 2010 ; Tabelin et al 2012a , 2012b , 2012c , 2013 , 2014a , 2014b , 2017 ; Tamoto et al 2015 ; Tangviroon et al 2017 ). Among these experiments, the column experiment has emerged as the preferred method for accurately simulating leaching in a realistic and long-term scenario, as opposed to the conventional batch experiment.…”

Pyrite oxidation mechanism in aqueous medium

“…Meanwhile, pyrite is the primary source of toxic metalloids and heavy metals in hydrothermally altered rocks and sedimentary rocks of marine origin . The main reason is that both transition metals and metalloids with similar properties to Fe and S tend to be incorporated into the crystal structure of pyrite …”

“…[4] The main reason is that both transition metals and metalloids with similar properties to Fe and S tend to be incorporated into the crystal structure of pyrite. [5,6] Pyrite oxidation is a major cause of acid mine (or acid rock) drainage (AMD or ARD), which is the biggest environmental problem in the mining and mineral industry as it can enhance the dissolution of rocks, acidification of aquifers, and mobilization of heavy metals. [7] The oxidation of pyrite involves water and oxygen consumption, where sulfuric acid will be formed.…”