Foreword
To May 27, 1989, Newmont's No. 1 gold cyanidation plant has entered its 25th year of production. The factory was originally designed to process 2000 tons of oxidized ore. In the past 20 years, the grinding capacity has been increased to 4,600 t / d. In 1985, the rated throughput was 3200 t/d, mainly due to some constraints in the subsequent countercurrent decanting circuit.
A plan was initiated at the end of 1985 to identify some of the constraints that exist in the plant by evaluating almost every component of every piece of equipment installed in the crushing and grinding system. After this evaluation, the biggest constraint was found in the 5-stage countercurrent decanting circuit. A decision was made at the end of 1986. It plans to expand the processing capacity of No. 1 cyanide plant, make maximum use of the processing capacity of the original equipment, and have developed the following two processes:
A: Add a carbon immersing circuit of 2000t/d scale and operate in parallel with the original 2600t/d countercurrent decanting circuit;
B: All 4600 t/d of material was treated by a carbon immersion process loop, but 4 of the original countercurrent decanter thickeners were used for tailings thickening.
Finally, the selected scheme B is considered to be relatively simple in operation, can reduce the production cost, and the investment is also minimal. This solution also has other advantages, including reduced solution loss and improved grades of coarse gold ingots.
In March 1987, the Kiborn Engineering Company of Canada and British Columbia approved the contracting of the political construction project. The carbon leaching plant was put into operation in October 1987.
First, the process overview
The No. 1 cyanide plant was originally designed to process 2000 tons of oxidized ore per day. The crushing system consisted of a Pioneer jaw crusher and a Symons crusher, which was closed with a Tylet shaker.
The ore is crushed to -l9mm and stored in one of the three l800t fine ore bins. These materials are then finely ground in a conventional ball mill system using a Marcy-type grid discharge ball mill , and the slurry is stirred for 15 hours in the leaching circuit. In the countercurrent washing and decanting system, the agitated pulp was further processed using five 3.75 m thickeners. The system is discharged from the decanter gold solution into precipitation system, where the gold cementation with zinc powder recovered. The gold mud is scraped regularly from the filter press, and after distillation, it is smelted into a crude gold ingot in an aluminum alloy furnace. In 1969, a 600t/d scale grinding and chlorination plant was added to treat carbonaceous ores that were produced simultaneously from the oxidized ore in the Carlin gold deposit. The only change to the subsequent process was the transformation of an oxidized ore leaching tank into a leaching tank of chlorinated carbonaceous ore. In 1983, another Marcy-type tared-row ball mill was added to accommodate the harder ore mined from the Bluestar and Maggie Creek mines. After the combination of oxidized ore and carbonaceous ore processing loop, the average daily throughput has dropped to between 2100 and 2000t. In l985, the ore produced from the Genesis mine was sent to the No. I cyanide plant for treatment at a rated capacity of 3,200 t/d.
Second, the optimization of existing equipment
Before making an investment decision, the production of the plant must be optimized, and maximizing the use of existing equipment is an important factor.
(a) broken
An evaluation of the crushing system revealed that the Symons cone crusher and Tyler screen had been damaged and replaced with new equipment of the same model.
Historically, the throughput of the mill has been significantly reduced in winter, mainly due to the fact that the crushing plant cannot provide feedstock for the ball mill, or that the feedstock is coarser. The installation of a soft rubber screen can solve the problem of broken winter. Rubber screen is highly adaptable. And it is not blocked like a normal wire screen.
(2) Grinding
The optimization of the grinding circuit is a plan being implemented. When the No. 2 cyanide plant in the Gold Quarry mine was put into operation in 1985, nearly half of the experienced operators and team leaders were transferred from the No. 1 cyanide plant to the No. 2 cyanide plant. Therefore, the training of the operator was started, and the process operation of the cyclone classification circuit was important.
The ball loading in all mills is increased from 40% to 50% of the mill volume to maintain the highest power draw.
When the crushing rate is increased due to higher mechanical efficiency, the crusher has a finer discharge product after the installation of the 1.25 mm screen, and does not reduce the efficiency. At this time, the standard 75 and 100 mm steel balls were replaced with 50 and 75 mm steel balls.
When the single corrugated liner was worn out, a double corrugated liner was placed in the middle of the two Marcy mills.
Third, countercurrent decanting circuit
After installing the second Marcy mill. The grinding capacity of the factory exceeds the design processing capacity of the thickener. The goal in this area is to maintain a very lean thickener feed concentration (15% to 17%). The factory conducts flocculation tests on a regular basis. The problem with thickeners is largely due to the high torque on the transmission and the often occurring extended double lanes. Thickeners require frequent repairs due to overload.
Investment cost: Consider the operation of the existing countercurrent decantation system at 2600t/d, and another carbon leaching plant with a treatment capacity of 2000t/d instead of constructing a treatment capacity of 4600t/d. The carbon leaching plant, which has been studied by Kilborn. Compared with the construction of a 4,600 t / d carbon leaching plant, the investment cost of building a 2000 t / d carbon leaching plant can be reduced by about 84,200 US dollars. The final plan was to build a 4,600 t/d carbon leaching plant, which began in March 1987.
According to the long-term experience of No. 1 cyanide plant, the main design data of the smelting process was determined and used in the process design of this expansion project.
Fourth, carbon immersion process design
No. 1 cyanidation treatment of two distinct types of ore - carbonaceous ore and oxidized ore.
The carbonaceous ore is ground to 6O to 200 mesh in fresh water. The cyclone overflow was removed with a high frequency Derrick screen (0.5 mm polyethylene mesh screen). The sieve is pumped to the chlorination circuit and the sieve is returned to the ball mill. The discharge pump of the chlorination circuit is pumped to the No. 1 and No. 2 leaching tanks, and cyanide is added after raising the pH, and the leaching time is about 24 hours.
The oxidized ore is ground to 60-200 mesh, and the cyclone overflow obtained from the two oxidized ore mills is discharged into a common storage tank, which is diluted and pumped to the de-mesh screen of the oxidized ore circuit. The miscellaneous screen consisted of four 1200 x 1200 mm "streamlined" Derrick screens (with a 0.5 mm polyurethane screen installed). According to the design, the sieve on the sieve is returned to the grinding circuit. This situation changed quickly after the carbon immersion system was put into production. The sieve above the sieve is now sent to the No. 2 thickener. The undersize of the oxidized ore removal screen is removed from the intermediate storage tank of the carbon immersion process, where it is combined with the treated carbonaceous ore and pumped to a new leaching tank in the charcoal immersion tank.
A new leaching tank is connected to six charcoal immersion tanks, each with the same volume. The height of the new leaching tank and the carbon immersion tank is 1.O5 to 1.38 m. Add the appropriate amount of coarse filler (overlay concrete) to increase the bottom of each tank (except the No. 6 charcoal dip tank). So that each tank has the same volume.
A 50 hp dual impeller Lightning mixer was installed in the leaching tank and the carbon immersion tank, and an air compressor was used to fill the leaching tank and the No. 1 and No. 2 charcoal immersion tanks. The slurry is directly flowed into the six carbon sequestration tanks connected in series from the leaching tank. The slurry flows from one tank to the next, and the height difference between the tank and the tank is 60 cm. The Derrick interstage screen was used to block the char and transfer them periodically. No. 1 charcoal immersion plant is the first factory to use this unique system. These interstage sieves are standard high-frequency sieves with a width of 1.2 m and a length of 2.4 m. There is a reverse slope of 12 ° C toward the discharge end, and the sieve is installed in the charcoal dip tank near the slurry surface. The slurry flows through the overflow weir into the sieve, using a polyurethane screen, the slurry reaches the chassis and enters the next charcoal dip tank, and the coarse carbon charcoal returns to the same charcoal dip tank. A Sala type vertical grooved impeller pump (suspended in the slurry) continuously lifts the charcoal and slurry in a countercurrent direction.
The gold-loaded charcoal was taken out from the No. 1 charcoal dip tank by a Sala type vertical groove impeller pump and discharged onto a separation screen. The on-screen product (loaded with gold charcoal) flows from the gold-loaded charcoal silo, and the gold-loaded charcoal accumulates a certain amount and is then transported to the desorption workshop located in the Gola Quarry mine for centralized treatment. The sieved product is returned to the No. 1 charcoal dip tank. The regenerated charcoal is transported back from the desorption plant by car, piled up in a silo, and then pumped to a No. 6 charcoal dip tank.
The carbon leaching tailings were passed through two 1.2×2.4m safety screens. Pump into the existing φ3.75m thickener and then discharge it into the tailings pond.
Now, some of the constraints behind the counter-current dumping loop have been eliminated, and the factory's goal is to achieve the highest throughput. Due to the variable hardness of the ore shipped to the No. 1 cyanide plant, the grinding grain size will be coarser in the oxidized ore processing circuit.
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