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Experimental Oxidative Dissolution of Sphalerite in the Aznalcóllar Sludge and Other Pyritic Matrices

^a Departamento de Ciencias y Recursos Agrícolas y Forestales, Universidad de Córdoba, Edificio C4, Campus de Rabanales, 14071 Córdoba, Spain
^b School of Environment and Natural Resources, The Ohio State University, 2021 Coffey Road, 210 Kottman Hall, Columbus, OH 43210-1085

View larger version (20K): [in a new window]   Fig. 1. Cross-section of the mechanical extractor used in the flow-through experiments (not to scale: syringe and sample tube diameter is 4 cm).

View larger version (15K): [in a new window]   Fig. 2. The pH of leachates of sludge and sludge–calcite samples as a function of the number of leaching steps in the flow-through experiment. Each value is the mean of two replicates. The standard error bar (two replicates) is not shown when its length is similar to or smaller than the size of the corresponding marker.

View larger version (18K): [in a new window]   Fig. 3. Cumulative amounts of (a) Fe, (b) Zn, and (c) S leached from sludge and sludge–calcite samples in the flow-through experiment. Each value is the mean of two replicates. The standard error bar (two replicates) is not shown when its length is similar to or smaller than the size of the corresponding marker. Despite the large standard errors for the sludge samples (solid symbols), the rates of leaching of either Fe, Zn, or S (as measured by the slope of the corresponding y–x regression line) did not differed significantly (P < 0.05) between replicates.

View larger version (30K): [in a new window]   Fig. 4. Diethylenetriaminepentaacetic acid (DTPA)-, acetate-, citrate-, and citrate–ascorbate-extractable Fe and Zn before leaching and after four and eight leaching steps (flow-through experiment): (a) Fe in sludge, (b) Fe in sludge–calcite; (c) Zn in sludge, and (d) Zn in sludge–calcite. Error bars are standard errors (two replicates).

View larger version (25K): [in a new window]   Fig. 5. The pH of leachates of pyrite, sphalerite, and 95% pyrite–5% sphalerite mixtures either with or without calcite as a function of the number of leaching steps in the flow-through experiment. Each value is the mean of two replicates. The standard error bar (two replicates) is not shown when its length is similar to or smaller than the size of the corresponding marker.

View larger version (22K): [in a new window]   Fig. 6. Cumulative amounts of (a) Fe, (b) Zn, and (c) S leached from pyrite, sphalerite, and 95% pyrite–5% sphalerite mixtures either with or without calcite as a function of number of leaching steps in the flow-through experiment. Each value is the mean of two replicates. The standard error bar (two replicates) is not shown when its length is similar to or smaller than the size of the corresponding marker.

View larger version (26K): [in a new window]   Fig. 7. DTPA-, acetate-, citrate-, and citrate–ascorbate-extractable Zn before leaching and after four and eight leaching steps (flow-through experiment) in (a) sphalerite, (b) sphalerite–calcite, and (c) pyrite–sphalerite–calcite mixtures. Error bars are standard errors (two replicates).

View larger version (26K): [in a new window]   Fig. 8. (a) Cumulative amounts of Zn leached from 95%–5% sludge–sphalerite mixtures either with or without calcite, and (b) extractable forms of Zn in 95% sludge–5% sphalerite mixtures mixed with calcite, as a function of number of leaching steps in the flow-through experiment. The standard error bar (two replicates) is not shown when its length is similar to or smaller than the size of the corresponding marker.

View larger version (22K): [in a new window]   Fig. 9. Amounts of Fe and Zn in the solution of suspensions of sludge and 95% sludge–5% sphalerite mixtures as a function of oxidation time. A logarithmic scale is used for the y axis to accommodate data better. According to the standard error values (not shown), differences between sludge and sludge + sphalerite are significant for Zn, but not Fe in solution.

View larger version (24K): [in a new window]   Fig. 10. Extractable Zn forms in the solids of suspensions of sludge and 95% sludge–5% sphalerite after 25 d of oxidation in the presence of calcite. Error bars are standard errors (two replicates).

View larger version (16K): [in a new window]   Fig. 11. Amounts of Fe and Zn in the solution of pyrite–sphalerite suspensions (1.8 g of solids in 35 mL of water) after 36 d of oxidation as a function of the percentage of sphalerite in the mixture.