Cyanide Bottle Roll Leach Test procedure

Cyanide bottle roll tests are the industry standard for the first step in evaluating gold recovery through cyanide leaching. They give valuable insights into expected recovery rates, reagent costs, and the necessary addition rates.

Equipment Needed:

Bottles with lids: To hold the test samples.
Tape: To securely seal the bottle tops.
Airlines: For adding air if needed.
Stirring device: To mix the contents (magnetic or mechanical).
Basic tools: Timer, pH meter, thermometer, and scale for measuring.
Leaching solution: The liquid used to extract metals (can be acidic, alkaline, or neutral).
Filter: To separate the liquid from solids (using vacuum or pressure).
Titration setup: To measure chemical concentrations.

Procedure:

Prepare the ore: Dry it and crush it to the required size.
Mix the solution: For example, dilute sulfuric acid with water to a specific strength.
Leaching: Add the crushed ore sample into a bottle, then pour in the leaching solution.
Stir and wait: Mix the sample for about an hour, ensuring the pH, temperature, and other conditions are right.
Filter: After leaching, filter the liquid to collect the metal-rich solution (leach liquor).
Wash and weigh: Clean the remaining solids and record their weight.
Analyze: Test the residue and the liquid for metal content.

Bottle Leach Procedure for Cyanidation.

Use at least 500g of material for the test, but 1000g is ideal. Make sure the bottle is large enough, and lay it on its side for the roller test. The lid should have a small hole to let air in, or you can use an air bubbler during the leach.

For kinetic tests, remove the bottle from the roller at intervals (2, 4, 6, 24 hours, and every 24 hours after that) to take samples. After each sample, add air or oxygen to simulate what happens during the process. If possible, measure the dissolved oxygen, as it’s crucial for the leach to continue. Just having enough cyanide isn’t enough if oxygen levels are too low.

It is recommended to conduct kinetic leaching tests. These are a bit more complex because you’ll need to replace the liquid you remove during sampling and account for the gold that’s removed. Make sure to use at least 3 points to create your kinetic curve: one after the second cyanide addition in your circuit (CIL tank 4), another at the end, and one more convenient point. Don’t cut the test short; if more time might lead to higher recovery, add more time. The balance sheet I provided has 8 points for tracking.

At each sampling point, measure the cyanide concentration. Your metallurgist and operators should be familiar with the titration process. Add enough cyanide to bring the concentration back to the target level. The circuit typically starts with 600-650 ppm, then adds cyanide midway to 300-350 ppm.

Before starting, ensure your sample is well-mixed (homogenized). If you don’t properly split your lab samples, the results might be inconsistent. Use samples from the flotation tail and check that your lab results match the actual plant performance. Test the water you’re using too—consider filtering off the old water and adding the intended test water. Run enough tests to confidently know what the expected results are for your circuit. Think of this as a calibration. If you’re unsure whether your lab tests match real-world results, be cautious with your conclusions. Make sure your sample heads match across tests. You should aim to reproduce a 95% match, though 92% is acceptable if you have coarse gold, which can be harder to replicate. Use duplicate tests to boost your confidence.

A test program begins by applying your current conditions to the new ore. If recovery is good, you’re done—congrats! If not, adjust one variable and run another test. It is recommended to test a known sample alongside the new one and also test another new sample with a higher cyanide concentration. Running only one test at a time can be slow, as it may take up to a week for results. Handling more than six tests at once can be challenging for one technician, although a well-prepared technician can manage up to 20 tests.

Key Tips:

Always wear eye protection when handling acid.
Slowly add acid to water, never the other way around, to avoid dangerous reactions.
Make sure to thoroughly wash the ore residues after leaching to remove all chemicals.

For longer tests (kinetic leaching), samples are taken over time to measure how much metal is extracted at different intervals. Regularly monitor and adjust cyanide and oxygen levels to keep the process going.

Make sure your test conditions mimic the actual processing environment as closely as possible and always take safety precautions when working with hazardous materials like cyanide.