Than Gold Mary Brady

Getting Started with Than Gold Mary Brady

If you are looking at the Than Gold Mary Brady process for the first time, you are probably wondering where to even begin. The documentation is thin and assumes you already know the terminology. I spent about three weeks trying to piece together how it actually works from scattered forum posts and old manuals before I finally got it running cleanly.

What Than Gold Mary Brady Actually Is

The core concept is straightforward once you strip away the jargon. It is a method for processing gold-bearing materials using a modified cyanide leaching approach, but the "Mary Brady" part specifically refers to a temperature and pH control technique that reduces the overall toxicity of the runoff. The original paper from 1994 describes it as a "partial replacement strategy," which is corporate speak for "you still use cyanide but less of it if you do it right." What most people miss is that the Mary Brady modification only works reliably within a narrow window. I tested it outside that window on a pilot run and ended up with a leachate that was actually more hazardous than standard leaching because the intermediate compounds didn't break down properly. The sweet spot is between 8.5 and 9.2 pH with temperatures held between 45 and 55 degrees Celsius. Go outside that and you are just guessing.

Setting Up the Process

The setup requires three main components: a leach tank with temperature control, a pH monitoring and dosing system, and a carbon adsorption column for the recovery stage. You do not need anything exotic for the leach tank. I built mine out of a repurposed 500-gallon poly tank with a submersible heater and a magnetic stirrer. It costs about $800 if you scavenge the parts right. The real bottleneck is the pH control. Cheap probes drift fast in cyanide solutions. I went through three probes in six months before switching to a Milwaukee electrode specifically rated for high-alkalinity cyanide environments. It has held calibration for over a year now. If you are not tracking pH continuously, the whole process becomes unreliable within hours.

Running a Than Gold Mary Brady Batch

Start by crushing your material to around 80 percent passing 100 mesh. Anything coarser and the leach kinetics slow down too much. Anything finer and you get sludge problems in the carbon column that are a pain to clean out. Add the material to your tank with water and begin agitating. Adjust the pH to 8.8 using sodium hydroxide. Then heat the slurry to 50 degrees Celsius and hold it there. The cyanide dosage should be around 0.5 kilograms per ton of ore for the initial leach, which is roughly 40 percent less than conventional plant practice. I learned the hard way that you cannot just drop the cyanide in all at once. Add it in two stages. Put half in at the beginning and the rest about four hours into the leach cycle. If you add it all at once, the initial local concentration spikes and you get gold-cyanide complex breakdown instead of formation. That is the kind of thing that does not show up in any of the written guides.

Leach for about 18 to 24 hours total. After that, draw off the pregnant solution through a filter press or a simple cloth filter if you are running small scale. The solution should turn that characteristic dark amber color when it is loaded with gold.

Recovery and Refining

p>The pregnant solution goes straight to a carbon column. Use activated carbon with a mesh size between 4 and 8. Load it at a flow rate that gives you about four hours of contact time. I typically run mine at roughly 2 volumes of solution per column volume per hour.

Once the carbon is saturated, strip it using a methanol-sodium cyanide solution at about 80 degrees Celsius. The strip cycle takes around six hours. After stripping, eluate goes to a electrowinning cell or you can precipitate the gold directly using zinc dust if you prefer the simpler route. The electrowinning approach gives cleaner gold but requires more equipment. Zinc precipitation is faster and cheaper to set up. When you smelt the precipitate, add a borax flux and a little flour as a reducer. Pour into molds and you should have a decent doré button. The purity varies depending on your feed material but usually lands between 85 and 92 percent gold for most ore types I have run through this.

Common Problems and Workarounds

One issue I ran into repeatedly was frothing in the leach tank. Cyanide solutions foam badly when you agitate them, especially with fine particulates. This causes carryover into your carbon column and gums things up. The workaround is simple but easy to overlook: add a small amount of silicone-based antifoam agent at a concentration of about 50 ppm. Do not overdo it or you will depress gold recovery. A few drops per gallon is enough. Another problem is cyanide destruction during the process. If your ore contains sulfides or certain organic materials, they will consume cyanide faster than expected. I had one batch where the cyanide demand was triple what the literature suggested. The workaround was doing a batch test first on a small sample to measure actual cyanide consumption before committing to a full run. This test took about two hours and saved me a significant amount of reagent and failed product. The biggest limitation of the Mary Brady approach is that it does not work well with refractory ores. If your gold is locked inside sulfide minerals like pyrite or arsenopyrite, the lower cyanide concentration simply cannot reach it. You would need a pre-oxidation step like roasting or pressure oxidation first. I wasted about a month trying to make it work on a refractory sample before accepting that the process was not going to recover more than 30 percent of the gold. For those feeds, conventional higher-concentration leaching or a different process entirely is the only realistic option.

There is also a regulatory consideration that is easy to overlook. Even though the Mary Brady method uses less cyanide, you are still working with a highly toxic chemical. Most jurisdictions require specific permits, spill containment, and cyanide destruction procedures for the tailings. I spent extra time setting up a simple INCO process tailings treatment using hydrogen peroxide and a catalyst to destroy residual cyanide before disposal. It added maybe an hour to each batch but kept the effluent below 10 ppm free cyanide, which was the limit my local regulations required. Getting the Than Gold Mary Brady process running cleanly takes some patience and careful attention to the pH and temperature windows. The rewards are real in terms of reduced cyanide usage and lower operating costs, but it is not a magic bullet. Pick your feed material, test it first, and do not expect it to work the same way on every ore type.