Process development testwork and detailed engineering are essential services 911Metallurgy Corp. offers separately. The equipment package described herein does not include any permitting, infrastructure, foundation, electrical, assembly, reagents/supplies or commissioning. These are all additional paid-for services we do offer if you need them.

The test is based on the treatment of a sample mass of typically 50 kg with a laboratory gravity concentrator. Three stages are used, the first on the sample crushed and rod milled to 100% -850 µm, and the next two on part of the tails of the previous stage, ground to achieve further gold liberation. Stage two is performed on typically 24 kg ground at 45-55% -75 µm, and stage three on 18 to 21 kg ground at 75-80% -75 µm.

The GRG tests are performed at increasingly lower feed rates and fluidization water pressures to match the finer feed, typically from 1000 g/min and 25 kPa for stage 1 to 400 g/min and 12 kPa for stage 3. These correspond to optimal settings as determined by extensive test work with both gold ores and synthetic feeds, but must be adjusted for gangue density. Because the test is optimized, it yields the maximum amount of GRG; actual plant recoveries will be lower, because of limitations in equipment efficiency and of the usual approach of processing only a fraction of the circulating load. Linking projected plant recovery to the results of the GRG test will be briefly discussed later.

For each stage, all of the concentrate and 600 g of tails are screened from 25 to 600 µm (the tail sample is wet screened first). The tail fractions above 105 µm are further pulverized prior to assaying. All of the concentrate screen fractions and up to one assay ton of tails are fire-assayed.

The test was used on more than 30 ore types, ranging from completely oxidized to complex sulphides. Some ores were tested twice with the regular procedure to assess natural variability. Additional work included performing either a single or all three gravity stages at final grind, to check the validity of the basic approach and explore possible simplifications. These additional tests are discussed at length in; they show that the progressive grinding (as opposed to testing only at final grind) is necessary to obtain the correct size distribution of GRG, as well as a measure of progressive liberation. Testing only at final grind normally underestimates the GRG content, because of over-grinding. Testing feed masses below 10 kg can result in a slight overestimate of GRG content for ores with a low sulphide content.

Concentration means increasing the amount of gold in ore or sediment, by selectively removing lighter particles. If employed effectively, concentration methods can eliminate or greatly reduce the need for mercury.

Before concentration can begin, ore must be crushed or milled to liberate gold particles from rock and to decrease grain size.

Concentration works best when grain size of the milled material or sediment is relatively consistent, so that most particles are of similar size. An appropriate grain size can be achieved using screens or sieves.

Once the gold-containing material has the appropriate grain size, one (or several) of the methods described below can be employed to concentrate gold bearing material.

Most concentration methods rely on the high density of gold relative to other minerals in ore or alluvium mixture. These are referred to as gravity methods, and this is the methods we intend to use for mining in Namibia .

Magnetic or chemical properties can also be exploited to enhance concentration.

Each mining operation is unique.  Concentration methods must be selected after considering factors such as the type of ore or sediment, other minerals present, gold particle size, and the availability of water and electricity.

Copper Mountain Corp has been involved with gravity concentration for the last years, having designed two distinct ranges of equipment; a semi-continuous Copper Mountain Corp range for installation into grinding circuits and the recently released  range for pre-concentration and scavenging in a wide range of mineral industries.

Understanding the Gold Centrifuge by Comparing it with a Sluice Box

Our biggest suggested units for this projects are the SB21 and SB38 semi-continuous , the SB38 being of 38 inches in bowl diameter with a concentrating surface area of 16720cm². The reason why I have included the surface area (in section 4 of this booklet there is a complete list of the  SB specifications with each individual units concentrating surface area) is that centrifugal gravity concentrators are similar to concentrating tables in that they can only treat a certain tonnage per given surface area. For this reason Falcon specifically designed deep bowls to ensure that a bigger tonnage could be treated using the same given bowl diameter.

A centrifugal device, acts as a pump forcing the material up the sidewalls. The faster that the bowl is spun, the higher the G-forces and hence the greater the tonnage that can be treated by the unit. Falcon operates its equipment at G-forces of 200Gs. Copper Mountain Corpengineer Abdon Narvaez, and his son Abdon M. Alejandro has also designed their bowls to be extremely plant friendly in the sense that the bowl is not fabricated from any exotic materials, in other words most of the maintenance can be carried out onsite without having to import exotic materials from Namibia . Below is an exploded schematic of the bowl on which I would like to focus your attention.

Spiral concentrators are specialized pans tilted on an angle with spiraled grooves. The spiral grooves in the pan lead toward the center where a hole is connected to a container to catch material.

A motor is used to rotate the pan continually as concentrate is fed onto the pan by an operator.  A pipe extending horizontally across the pan sprays water along the surface of the pan as the concentrator spins. The water washes lighter particles down the spiral concentrator into a bucket while denser particles, including gold, are carried by the spiral grooves toward the hole in the center of the concentrator.

After this process is repeated multiple times, the operator is left with a high grade concentrate, and often liberated gold. Spiral concentrators are relatively easy to operate but do represent a larger capital investment than panning or sluices.

Falcon has spent a major amount of time adhering to our motto, “designing simple and cost effective equipment that can be easily maintained onsite”. The riffles are manufactured from 304 stainless steel and are independent of the bowl. This means that the riffles can be replaced at a fraction of the cost without having to purchase an entire new bowl. The bowl has also been designed to be a long wear life item in that it has a sacrificial rotor baffle that can easily be replaced, and increased rubber thickness in the areas where there is a change in direction of the pulp i.e. adjacent to the impeller. Falcon rarely replaces bowls and prides itself in this unique design which is definitely a cost advantage to you the client.

Falcon prides itself in the recovery of very fine gold particles (below 10 microns), this can only be achieved with the use of low water pressures to fluidize the concentrate riffles (50 – 80 kPa) and with high outward G-forces (200Gs). Other equipment encountered in the industry make use of high water pressures and lower G-forces resulting in the ejection of fine gold from the collected concentrate.

Vortex concentrators use a rotating flow of water to separate lighter materials from a concentrate and remove them via a raised drain hole.

A vortex concentrator is a circular tub with water input on the side of the tub and a raised drain in the center. The tub is filled with water until it reaches the level of the drain hole. Then concentrate is added in a thin layer around the bottom of the bowl. Water is then pumped into the side input, creating a rotating vortex of water that drains in the center. The vortex pulls lighter material up from the bottom of the bowl and out the drain hole.  Dense materials such as gold remain in the bottom of the tub. After the miner sees only gold left on the bottom of the bowl the water source is turned off and the gold is ready to be removed.

Miners must pay attention to the amount of water flow going into the tub. If it is too great the velocity of the water will carry gold particles out of bowl and this will lead to losses of gold. When vortexes are operated correctly, the result is a fine gold concentrate that is usually very high grade. Vortexes are easy to operate and are good at capturing fine gold that is hard to extract through other methods.

Shaking tables are elevated tables tilted to one side with raised ridges running horizontally down their length. Mineral feed (crushed ore or sediment) and water are released at one end of the table. The water washes the feed down the table. As the material is washed down the table, specialized grooves trap gold and direct it to collection points on the side of the table as lighter minerals are washed away. During this process, the table is continually shaken by a motor to agitate the material and aid in the separation of gold particles.

Shaking tables are very effective and can concentrate sizeable amounts of ore at a time, providing high grade concentrates and liberated gold, but they are also relatively expensive and require some experience to operate.

Process Introduction

Heap leaching (HL) is a flexible and economic mineral processing method, commonly used to extract gold from low-grade gold ores. In this process, ore is firstly crushed to fine particles. By spraying leaching solution to the large piles, the gold-containing solution is leached. Then used the method of carbon adsorption, zinc powder displacement device and so on to separate gold from the liquid.

Application

Heap leaching method is always used for low-grade ore, small gold mine, or both. These ore can not to process by using the conventional method.