1. Sulfuric, Sulfurous, and Methanesulfonic Acids

1. SULFURIC, SULFUROUS, AND METHANESULFONIC ACIDS

Each split was weighed out in a glass bottle of known weight. Bottles were partly filled with water and acid was added with an Eppendorf pipet to a concentration of 10 g/L for sulfuric and sulfurous acids and 20 g/L for methanesulfonic acid. The sulfurous acid used had a purity of 6.62% and was measured out in a graduated cylinder, with nearly 50 mL being required to achieve a concentration of 10 g/L for the samples. Ferric sulfate was weighed out and added to an Fe3+ concentration of 5 g/L. Each bottle was topped up with deionized water and pH was measured with a pH meter calibrated at the beginning of the bottle roll test. After pH measurement, enough deionized water was added to each bottle to bring the total pulp to 20% solids. The bottles were then placed on rollers and rolled at 60 rpm.

At 2- and 6-hour breaks, the bottles were removed from the rack and the solids allowed to settle. A sample was pipetted from the supernatant leach liquor of each bottle into a small beaker, and then filtered and transferred to a labeled test tube using a filter-tipped syringe. The pH was measured again. For sulfuric acid, bottles with a pH above 1.8 were injected with additional H2SO4 0.1 mL at a time until measured pH dropped below 1.8. The pH’s for sulfurous and methanesulfonic acids were allowed to increase above 1.8 without further acid addition. After this, the bottles and pulps were topped up with deionized water to the target weights and placed back on the rollers.

The same procedure was followed for sampling and pH measurement at the end of the test (24 hours). For sulfuric and sulfurous acids, one additional 10mL sample was taken and titrated in deionized water with 1 M NaOH and 6 drops phenolphthalein (and 6 drops H2O2 in the case of sulfurous acid) to ascertain remaining acid concentration. No titration was performed for methanesulfonic acid. The residues were drained on filter paper and rinsed with deionized water, then allowed to dry.

2. CYANIDE

Each split was weighed out into an empty glass bottle of known weight. The bottles were partly filled with water and their natural pH was measured with a pH meter calibrated at the beginning of the test. Lime was weighed out on a precision scale and added to each bottle 0.05 g at a time until pH reached 11. Bottles were rolled at 60 rpm on a roller rack for 5 minutes, then pH was measured again. If pH had fallen below 10.8, more lime was added and the rolling test repeated until all pulps had a pH > 10.8 even after 5 minutes’ rolling. Cyanide was weighed out and added to a concentration of 1000 ppm. Each bottle was brought up to target weight for 40% solids with deionized water and rolled at 60 rpm.

At the 2- and 6-hour breaks, the bottles were removed from the rack and solids allowed to settle. Titration beakers were prepared with 50 mL deionized water, 2 drops of 10% NaOH, and enough rhodanine to tint the solution yellow. When the solids had settled in each bottle, a 10-mL sample was pipetted from the supernatant leach liquor and filtered into a labeled test tube. A second 10-mL sample pipetted from each leach liquor was deposited in one of the titration beakers and titrated with AgNO3 over a magnetic stirring plate.

The pH of each bottle was measured and, if below 10.8, lime was added 0.05 g at a time until pH rose to 11 and remained above 10.8 after 5 minutes’ rolling. Additional NaCN was weighed out and added to each pulp to bring the concentration back up to 1000 ppm. Each bottle was topped up to the target weight with deionized water and rolled again. This procedure was followed for the 24-hour check as well, with the exception of the reagent addition and further rolling. Residues were drained on filter paper, rinsed with deionized water, and then dried.

3. THIOUREA

Thiourea solution was made up in advance in 1L volumetric flasks. Each flask was rinsed with deionized water and partly filled with deionized water. Ten grams of thiourea and enough ferric sulfate pentahydrate to make a solution of 3 g/L Fe3+ were added to each flask along with 1 g sodium metabisulfite and 1.630 mL (3 g) 98% H2SO4. The flasks were stirred on magnetic plates until all solids had dissolved. Stir bars were then removed and enough deionized water added to bring the solution up to the mark on the volumetric flask. The flasks were then shaken, covered, and inverted to mix the solution.

Splits were weighed into empty bottles of known weight and thiourea solution added until 40% solids was reached. Eh and pH were measured and the meters rinsed into a waste bucket. The bottles were rolled at 60 rpm.

At 2 and 6 hours, the bottles were removed from the rack and the solids allowed to settle. Titration beakers were prepared with about 50 mL deionized water, 20 mL of 2N H2SO4, and a squirt of starch solution. Once the solids had separated enough, 12mL of sample were pipetted from the supernatant leach liquor in each bottle. After filtration, 10mL were placed in a test tube and the remaining 2 mL were added to the titration beakers. The solutions were titrated with KIO3 and the bottle replenished with thiourea according to the results. Sodium metabisulfite was also added to 1/10 the amount of thiourea. The pH of each bottle was measured and 2N H2SO4 was added in 0.1-mL increments until pH fell below 2. The Eh of each sample was measured and each bottle was topped up to the target weight with deionized water. This procedure, except for reagent addition, was also followed for measurement and sampling at the 24-hour end of the test. Residues were drained on filter paper, rinsed with deionized water, and dried.

GLYCINE

Each split was weighed into an empty bottle of known weight and about 100-150 g deionized water was added to it as well. Glycine was added to a concentration of 0.5 M and peroxide was added by weight to 3% of the solution. The pH was measured with a meter calibrated at the beginning of the test and 50% NaOH was added in 2mL increments until pH was > 11 and remained > 11 after 5 minutes of rolling at 60 rpm. After Eh measurement, the bottles were rolled.

At 2 and 6 hours, the bottles were removed from the rack and the solids allowed to settle. A neutral formalin solution was made by titrating formaldehyde and phenolphthalein with 0.2N NaOH. Sample beakers were prepared with 18 mL deionized water. When the solids in the pulps had settled, 10 mL samples were pipetted from the supernatant leach liquor and filtered into test tubes. Using an Eppendorf pipet with a fresh tip, 2 mL of each sample was transferred to the titration beaker. The pH of the titration sample was measured and adjusted by HCl and NaOH until it reached 6.8 ± 0.5 pH units. Once the target pH was reached, a magnetic stir bar, 10 mL of neutral formalin, and 6 drops of phenolphthalein were added to each beaker. Each sample was then titrated with NaOH until the phenolphthalein turned and remained a dark fuchsia color. Enough glycine was then added to each bottle to bring its glycine concentration back to 0.5 M, and NaOH was added until pH remained above 11. After Eh measurement, the bottles were rolled again. This procedure was also followed at the end of the test at 24 hours, except that no reagent was added and there was no further rolling. Residues were drained on filter paper, rinsed with deionized water, and dried.