CARBOx Processing

The CARBOx process is based on burning the carbon to reduce the volume for precious metal recovery. Precious metals remain with the ash and the burner exhaust is processed to prevent mercury emissions to the environment. The oxidation system has multiple stages of scrubbing for mercury removal from the exhaust gas.

CARBOx Flowchart

Feed

Feed to the carbon burner arrives in bulk bags. The bags are hoisted by a crane and trolley to a bag dump station. The feeder is kept full at all times.

Carbon Burner

The carbon burner is a fluidized bed reactor, the heart of the process. The carbon burns as it enters the burner leaving the non-combustible ash behind. The heavier fraction of the ash stays in the bed to serve as a heat sink and temperature moderator. Lighter ash is carried out the with the exhaust gas.

Gas Cooling

The cyclone overflow contains most of the mercury and a minimal amount of the precious metals. The off gases are cooled to less than 250 F with a water-cooled heat exchanger.

Gas Scrubbing

Mercury and any remaining dust are removed in a series of scrubbers and a final activated carbon filter. The first stage scrubber is a venturi scrubber designed to remove essentially all of the dust. The gas is cooled to 85 F in this stage.

Water treatment

The pH of the solution collected in the water surge tank is adjusted. After the pH adjustment, the water is treated chemically to ensure all dissolved solids are removed from the water.

Cooling water

The gas cooler described above requires cooling water to remove the heat from the exhaust gas. The cooling water is supplied by a cooling tower where the water is cooled by evaporative cooling. Softened water is supplied to maintain the cooling water level. A small amount of water is removed to limit the dissolved solids concentration.