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The Carbon Converter is a modular, self-contained unit for converting up to 600kg of carbon per day into a fine dry ash. Dirty, wet carbon fines are loaded directly into the roasting chamber and feather-light carbon ash is fully captured as a dry product. A three-stage exhaust scrubbing system fully captures mercury to satisfy emission standards of every U.S state and foreign country. Complete gold and silver recovery has been demonstrated. For more information, download the Carbon Converter brochure.

Process Description


Two (2) interchangeable bottom sections of the furnace allow for semi-continuous operation. The semi-continuous batch system is easily operated by one person through a sophisticated PLC interface. 

The process begins as carbon fines are loaded into the feed hopper. An automated conveyor then transfers the fines material to the top of the furnace. The carbon is continuously and evenly distributed over a thick bed of silica sand by a rotating distributor head. A burner is used to preheat the furnace. Hot air is pulled down through the carbon which combusts to provide operational heat. Excess water is evaporated, and the carbon begins to ash. 

Carbon is continuously burned in the furnace at a temperature of 700 degrees celsius, until the level of accumulated ash alerts the operator to exchange bottom sections for the next ashing cycle. The carbon ash is collected in a specialized high temperature vacuum, and easily removed for gold and silver recovery. 

The hot exhaust gas flows through a series of two (2) venturi/water scrubbers, using water at ambient temperature to remove the bulk of volatiles, including most of the mercury. Mercury is collected in a conical sump below each scrubber. Water for this stage is process solution, flowing into the system and discharging back into the leach process. As a final polishing step, the cooled exhaust gas passes through a tank filled with sulfur-impregnated carbon to remove any trace amounts of mercury from the exhaust gas stream. Once the ashing cycle is complete, the ash, which has been roasted at high temperature, contains no mercury. 

Frequently Asked Questions

Q: How sensitive is the process to variability in the feed?

A: The process is semi-continuous batch, with the batch cycle time dependent on the feed material. We have seen cycle times as short as one (1) hour and as long as twenty four (24) hours. Feeds which are very high in clay (say 70% clay, 30% carbon) might require agglomeration, which can be done by the operator in a simple drum concrete mixer. 

Q: What test work is recommended for each site/carbon product?

A: The test work will include assaying for gold/silver, carbon and moisture content, and some basic physical characterization (visual inspection and screening). The test work will require gathering representative samples of the waste carbon on site.

Q: What is the actual product I'm getting from the unit? How much product does it yield?

A: The product will be a mix of carbon ash containing the gold, a small quantity of silica sand from the hearth, and any non-combustible material that was fed with the carbon. Total ash produced per furnace cycle depends on how much non-combustible material is present in the feed.

Q: How do I treat the ash to get my gold?

A: If the plant is a CIP/CIL: The ash product is cyanide soluble when finely ground and can be fed into an agitated leach circuit to leach and recover the gold. The ash can also be smelted directly.

If the plant is a Heap Leach/CIC: A small leach circuit can be set up to periodically feed high-grade solution to your existing strip plant, or depending on the capacity of your smelting furnace(s), the product can be smelted directly. 

Q: How much floor space/footprint does the unit require?

A: The installed Carbon Converter footprint with the feed system is approximately 6m x 6m. Additional space around the perimeter is required for proper access for operation and maintenance. A high temperature vacuum is also included on a mobile skid and is approximately 1.3m in diameter, which may have to be moved around the perimeter of the Carbon Converter.

Q: How is mercury controlled/captured?

A: The hot exhaust gases from the furnace are cooled and treated with two wet venturi scrubbers and associated tanks in series, which drop mercury for periodic collection from the tanks. The exhaust exiting the second venturi is fed through a bed of sulfur impregnated carbon to capture any residual mercury. Mercury-loaded carbon from the carbon scrubber can be fed to the carbon converter, so that the only mercury discharge is metallic mercury from the collection tanks. 

In some cases, it is possible that some minor quantity of condensed mercury can be carried out with the cooling solution stream. If this is not acceptable, then filters can be installed on the solution outlet.

Q: What are the utilities requirements?

A: The unit will require approximately 70kW attached electrical power with a nominal usage of 25kW. The unit has a 400,000 Btu/hr (100,000 kcal/hr) burner, in which fuel can be natural gas, propane or diesel. Approximately 20 gpm @ 40 psi of cooling/scrubber solution is required, which can be process solution or raw water.

Q: What is the cost to run the unit?

A: Operating costs can range from $50,000 to $150,000 per year, excluding labor costs. These costs depend in large part on the nature of the feed. We will evaluate your carbon and estimate the consumables usage and cost.

Generally, with clean carbon and long furnace runs, we expect minimal operator time will be required. With dirty carbon and more difficult materials handling, one operator may be required full time, resulting in higher labor costs. KCA will help define these costs more accurately as information is received regarding your carbon. 

Q: I need to process more than 600kg/day. Do you have a larger unit?

A: Currently, there is one size unit, but multiple units can be provided to reach the desired throughput. The unit is of a modular design that can be easily setup, taken down, and packed into a 40ft shipping container. The size is convenient for a single person to operate one or multiple units.

Q: Does the unit have to be installed indoors?

A: The unit is designed to be installed indoors but can be installed outside with proper protection from the elements.

Q: How soon can the unit be delivered?

A: Upon receipt of the purchase order and down payment, KCA can be ready to ship from our shop in Reno in about 16 weeks. 

Q: What is your warranty/guarantee on the equipment?

A: KCA will guarantee the equipment for a period of 12 months after completion of commissioning. The equipment is warranteed against component failure as a result of faulty equipment or construction, and KCA will repair or replace components at KCA's cost and responsibility. KCA will include one follow-up visit at no charge after commissioning to assess the performance of the unit and perform repairs/adjustments if necessary. 

*For additional services/equipment offered by KCA, visit the home page.