The San Ramon project in Colombia is designed around a whole-ore carbon-in-leach (CIL) process circuit with a nominal throughput of 1,000 tonnes per day, featuring a crushing plant, grinding circuit, agitated leaching, carbon recovery, and tailings pressure filtration.
Article Body
The proposed San Ramon processing facilities include a complete circuit to process gold-bearing material from an underground mining operation. During the early stages of the study, an economic trade-off was conducted between whole-ore leaching and whole-ore flotation with re-grind followed by intensive leaching of the float concentrate. Based on relative cyanide consumptions and recoveries as determined in laboratory test work, the economics slightly favored the whole-ore leach method. Consequently, the whole-ore leach (CIL) circuit was chosen for processing the ore. The layout has been designed to incorporate an additional ore processing line to at least double plant throughput in the future. The basic unit operations include primary crushing, SAG milling, ball milling, cycloning, pre-leach and CIL tanks, a carbon recovery plant with elution and reactivation, tailings pressure filtration, and water distribution systems.
The crushing plant is designed to operate one 12-hour shift per day, seven days per week, with a design crushing production rate of 133 tonnes per hour at 75% availability. All crushing operations occur during the day shift to prevent excessive noise levels at night. Run-of-mine material is fed to a ROM feed bin with a stationary grizzly deck having an aperture of 300mm by 300mm. Oversize material passes through a vibrating grizzly and a primary jaw crusher. Crushed product is conveyed to a secondary screen and cone crusher in closed circuit, with screen undersize at a P80 of approximately 11mm representing the final product, which is stacked on a crushed-ore stockpile. It is estimated that about one-half of the feed material might be re-handled from the stockpile area by a front-end loader.
Critical Data
| Parameter | Value | Unit | Notes |
|---|---|---|---|
| Annual Tonnage Processed | 360,000 | tonnes | Equivalent to 1,000 tpd |
| Crushing Operation | 12 hours/shift, 1 shift/day, 7 days/week | , | Day shift only to reduce noise |
| Crushing Area Availability | 75 | % | Design value |
| Crushing Production Rate (Design) | 133 | tph | , |
| Grinding Product Size | 80% passing 74 | microns (200 mesh) | Cyclone overflow |
| Pre-leach Tank | 1 | tank | Air-sparged |
| CIL Tanks | 5 | tanks | Air-sparged, counter-current carbon movement |
| Gold Recovery | 93 | % | At 48 hours of leaching |
| Thickener Underflow Density | ~45 | weight % solids | With flocculant addition |
| Tailings Filter Presses | 2 | units | One operating, one standby; each handles 100% of tailings |
Overview
The San Ramon project proposes a conventional whole-ore CIL processing plant to treat gold-bearing material from an underground mine in Colombia. The process design criteria are summarized in Table 17.1 of the technical report. The plant is designed for a nominal throughput of 360,000 tonnes per year (1,000 tonnes per day). Grinding is achieved through a SAG mill and ball mill in closed circuit with cyclones, producing a cyclone overflow with 80% passing 74 microns. Additional leaching occurs in the grinding thickener feed mix box, grinding thickener, and agitated-leach tanks. A single pre-leach tank and five CIL tanks provide the agitated leaching capacity, with gold recovery estimated at 93% after 48 hours of leaching.
The process selection was based on laboratory test work comparing whole-ore leach versus whole-ore flotation with re-grind and intensive leaching of concentrate; the whole-ore leach method was chosen due to slightly better economics related to cyanide consumption and recovery.
Key Process Stages
Crushing begins with a ROM feed bin equipped with a scalping grizzly (300mm by 300mm aperture). A vibrating grizzly and jaw crusher reduce the ore, which is then conveyed to a secondary screen and cone crusher in closed circuit. Screen undersize at P80 of approximately 11mm is the final crushing product, stacked to a crushed-ore stockpile. The crusher is sized to operate one 12-hour shift per day, and surplus capacity allows for periodic production of road gravel during part of a second shift about one day per week.
Grinding and classification use a SAG mill followed by a ball mill in closed circuit with hydrocyclones. The cyclone overflow must achieve a ground product particle-size distribution of 80% passing 74 microns (200 mesh). The cyclone feed pressure is maintained as needed to achieve the required particle size. The cyclone overflow reports to a grinding thickener via a feed mix box where additional leaching occurs.
Leaching and CIL are performed in an agitated-leach circuit with one air-sparged pre-leach tank and five air-sparged CIL tanks. Slurry from the grinding thickener is leached with cyanide, and carbon is added to the CIL tanks, advanced counter-current to slurry flow by five vertical submersible pumps in each tank. Leached slurry passes over a carbon safety screen before discharging to a wash thickener.
Carbon recovery involves elution and reactivation. Carbon is transferred between unit operations by recessed impeller pumps to minimize attrition. Loaded carbon is stripped using a heated pressure vessel; strip solution is discarded every third strip cycle, with fresh solution made up in the strip-solution tank. Carbon is reactivated in a rotary kiln at elevated temperature with an off-gas scrubber to capture mercury. Carbon fines generated during movement and regeneration are collected and sent off-site for residual metal recovery.
Tailings handling uses a thickener to recover process water. The thickener has been oversized to accommodate a second processing line. Underflow at approximately 45 weight percent solids is pumped to a filtration plant with two recessed plate filter presses (one operating, one standby). Filter cake is conveyed to temporary storage and ultimately to a tailings storage facility. Excess water is pumped back to the process pond for reuse.
Reagent handling and metallurgical control complete the plant. Reagents include sodium cyanide (as dry powder in bulk bags), caustic soda, copper sulfate pentahydrate, and hydrochloric acid. Cyanide solution is metered to the grinding and leaching circuits. Sampling equipment for solids and liquids is located throughout the plant, with primary metallurgical control obtained from the cyclone-overflow head sample and final tailings sample.
Additional Interesting Data and Summary
The process plant layout has been designed to incorporate an additional ore processing line to at least double throughput in the future. The grinding thickener is oversized to accommodate this expansion. The crushing circuit has sufficient surplus capacity to produce road gravel for on-site road maintenance by operating part of a second shift one day per week. During gravel production, secondary-screen undersize is redirected to a dedicated gravel-stacking conveyor by a diverter chute.
Carbon regeneration is recommended for all carbon batches before returning to the CIL circuit. If carbon is not scheduled for reactivation, it is pumped directly to the final CIL tank. The carbon reactivation kiln off-gas system is designed to remove over 99.5% of particulates in exhaust fumes via a baghouse. Carbon fines are collected in plastic-lined containers and eventually sent off-site for residual metal recovery. New carbon is supplied in 500 kg bulk bags and periodically added to the CIL circuit.
The detoxification process uses the Air/SO2 method for cyanide destruction, with copper sulfate pentahydrate as a catalyst where needed. Hydrochloric acid is used in the acid wash circuit and for alkalinity protection when mixing cyanide. Furnace off-gas collection includes a hood, baghouse, and induced-draft exhaust fan.
Key Processes
- Whole-ore carbon-in-leach (CIL) leaching with air-sparged pre-leach and CIL tanks
- Primary crushing with jaw crusher and secondary crushing with cone crusher in closed circuit
- SAG mill and ball mill grinding in closed circuit with hydrocyclones
- Grinding thickener to recover additional leaching and thicken slurry
- Carbon counter-current transfer using vertical submersible pumps and recessed impeller pumps
- Carbon elution and thermal reactivation with off-gas mercury scrubbing
- Tailings pressure filtration using recessed plate filter presses
- Air/SO2 detoxification of cyanide
- Process water recovery and recycling from tailings and thickener overflow
Source: San Ramon Deposit , Amended Technical Report and Preliminary Economic Assessment, Red Eagle Mining Corporation, March 31, 2014.
Editorial Note
The source text contains a minor internal inconsistency: it states that the circuit includes a grinding thickener for additional leaching, and elsewhere that leaching also occurs in the grinding thickener feed mix box, but the relative configuration and the exact number of pre-leach tanks (stated as one) are consistently presented. The report also notes that elution and reactivation, and carbon regeneration details are described, but the specific regeneration kiln temperature is not stated as a numerical value in the source excerpt. A separate note: the source mentions a feed material re-handling estimate of one-half from the stockpile area, which is stated as an assumption rather than a design criterion.
Project website: San Ramon Deposit, 2014 Technical Report
