Mineralogical-chemical techniques (XRD, SEM/EDX, WDXRF) and a sequential selective extraction procedure were applied to mine-waste materials and stream sediments from the Baccu Locci stream catchment (Sardinia, Italy) affected by serious As contamination as a consequence of past mining. Results indicate that solid-state speciation of As is mainly dominated by the presence of Fe(III) hydroxides (arsenical ferrihydrites with various Fe/As molar ratios) Occurring as coatings of silicate brains. in which As is contained as sorbed or co-precipitated species. Scorod te (FeAsO(4)(.)2H(2)O) is common too, whereas arsenopyrite is generally subordinate but, owing to its relatively rapid oxidation, environmentally significant. Moreover, some unidentified arsenates of Ca-Fe or K-Fe were also detected. Arsenic contained in these phases is slowly, but Continuously, released in relatively small amounts through three main mechanisms: (1) oxidation of residual arsenopyrite to scorodite; (2) decomposition of scorodite into a hydroxide or oxide of Fe(III); (3) desorption/release from Fe(III) hydroxides. Decomposition Of the unidentified arsenates is also probable, e.g. Ca-Fe arsenate --> calcite + Fe(III) hydroxide + As release. The flotation tailings are widely scattered and distributed in the middle-lower Baccu Locci stream catchment, and represent the most dangerous As-generating contamination source in the study area
Mineralogical controls on arsenic mobility in the Baccu Locci stream catchment (Sardinia, Italy) affected by past mining
FRAU, FRANCO;ARDAU, CARLA
2004-01-01
Abstract
Mineralogical-chemical techniques (XRD, SEM/EDX, WDXRF) and a sequential selective extraction procedure were applied to mine-waste materials and stream sediments from the Baccu Locci stream catchment (Sardinia, Italy) affected by serious As contamination as a consequence of past mining. Results indicate that solid-state speciation of As is mainly dominated by the presence of Fe(III) hydroxides (arsenical ferrihydrites with various Fe/As molar ratios) Occurring as coatings of silicate brains. in which As is contained as sorbed or co-precipitated species. Scorod te (FeAsO(4)(.)2H(2)O) is common too, whereas arsenopyrite is generally subordinate but, owing to its relatively rapid oxidation, environmentally significant. Moreover, some unidentified arsenates of Ca-Fe or K-Fe were also detected. Arsenic contained in these phases is slowly, but Continuously, released in relatively small amounts through three main mechanisms: (1) oxidation of residual arsenopyrite to scorodite; (2) decomposition of scorodite into a hydroxide or oxide of Fe(III); (3) desorption/release from Fe(III) hydroxides. Decomposition Of the unidentified arsenates is also probable, e.g. Ca-Fe arsenate --> calcite + Fe(III) hydroxide + As release. The flotation tailings are widely scattered and distributed in the middle-lower Baccu Locci stream catchment, and represent the most dangerous As-generating contamination source in the study area
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