Arsenic incorporation into pyrite at ambient environmental conditions: a continuous-flow experiment

Pyrite was synthesized in the presence of arsenite, As(III), at concentrations approaching those in ambient environments, under controlled, monitored, anoxic conditions in a continuous-flow reaction system at pH 6 and 25°C. During the continuous pyrite growth in these experiments, a continued uptake of arsenic by pyrite was observed. No unequivocal effect of As(III) on the amount of pyrite or on the textures formed was observed. The results presented here demonstrate that a continuous-flow approach to experimentation allows the investigation of contaminant uptake at realistic concentrations. The net result of the reactions studied is the continued fixation of arsenic in pyrite, and the formation of arsenian pyrite. The uptake of arsenic by continuously growing pyrite strongly suggests that arsenic cannot be re-released into solution, unless pyrite is oxidatively dissolved. Furthermore, the synthesis of arsenian pyrite at ambient environmental conditions is in agreement with authigenic arsenian pyrite formed in, for example, marine sediments.