Presentation on theme: "Experience Scotia, a Utah based corporation was founded to meet the needs of industry. Scotia provides innovative engineering and fabrication services."— Presentation transcript:
Experience Scotia, a Utah based corporation was founded to meet the needs of industry. Scotia provides innovative engineering and fabrication services in all disciplines to suit our client's requirements. Nearly a century of combined experience enables Scotia to offer state-of-the-art designs and equipment to serve industry.
The first designs of carbon columns utilized resin columns used for Uranium recovery. These columns has an length to diameter aspect ratio of at least 3 to 1. The resin columns required this high aspect ratio since the fluidization rates of resin are fairly low (10 to 20 gpm/ft 2 ). The high ratio allows for 200 to 250% bed expansion. These types of columns were utilized at Pinson and Dee Gold.
As the design was scrutinized with was determined that since activated carbon of a similar size has significantly higher fluidization rates (45 gpm/ft 2 ); designs were changed towards a ratio of 1.0 to 1.3 height to 1 diameter. (The ratio normally is 1.3 to 1 on columns less than 10 in diameter and then reduces to 1 to 1 on diameters over 10)
Activated carbon added to the CIC system is usually of a 6 x 12 mesh or 6 x 16 mesh size. As the material is used the carbon breaks down and the size distribution changes. The carbon process contains a sizing screen that removes any carbon below a specified size. For 6 x 12 mesh carbon that size is 16 mesh and for 6 x 16 carbon that size is 20 mesh.
If you look at the carbon particles, you will notice the are somewhat platey. They have narrow depth, which is indicative of the origin from coconut shells. This long, wide but not thick aspect allows for the higher fluidization rates as compared to the regular spherical shape of ion exchange resin. One of the main objects in the design of the carbon columns is to fluidize the carbon without pushing it out of the column. Normally, a carbon column is designed for about 70% fluidization. This design allows higher flows if required. But as the carbon becomes more used the size distribution becomes finer and some of the smaller particles are fluidized complete out of the column and wind up in the solution distribution plenum.
Scotia International of Nevada has been making carbon columns for over 23 years. About 12 years ago, we looked at the way our clients were using the columns and came up with a design change. Many of the columns were being placed in high rainfall areas and clients were requiring larger columns to accommodate the rainy seasons. This design requirement meant that the operations were using all of the design factor and actually were adding extra trains of columns. To accommodate, the increased flow requirements, Scotia designed the flaired column. This column utilizes a one foot flair in the column in the top third of the column. The flow for an eight foot column is 2200 gpm but a nine foot columns flow is 2800 gpm. But at 2200 gpm, the fluidization rate drops below 40%, which can cause silting problems so you would not build a system at that size for only 50% usage. The flaired column allows you to operate under both high and low flow conditions.
When Scotia looked closer at the flair design, we found that there were benefits to the flair design in all column applications. The flaired section of the column helps to keep and carbon that has been broken during carbon advancement transportation within the column. This occurs since the large diameter of the flaired section decreases the cross-sectional velocity. This velocity decrease allows more small carbon particles to stay within the columns working area. When they particles stay within the working area, then those particles can be move with the larger particles, go to stripping and have the gold removed and be removed after stripping by the sizing screen. This keeps the operator from sending partially load carbon to the carbon fines. Since only a portion of the gold on the carbon fines is recovered, decreasing the portion of loaded carbon going to this destination increase gold recovery.
For a 2000 gpm set of carbon columns, the amount of fine carbon captured is 20 tonnes per year. Stripped carbon grade is usually 100 grams per tonne. But normal carbon fines grade is 6 oz/t. The higher grade of the carbon fines is associated with the carbon captured on the safety screen. Carbon captured on the safety screen is not recycled since it will just elutriate out again, so it is sent to the carbon fines system.
So if the carbon fines can be retained in the column and the stripped before they are removed from the system. The carbon fines grade would be reduced to the stripped carbon grade. That is, 20 tonnes at 200 g/t equals 4 kg/yr or 129 oz 20 tonnes at 100 g/t equals 2 kg/yr or 64 oz 65 oz x $500 per oz = $32,500 per year savings
An additional benefit of the flair is realized during the time that carbon is advanced. When the carbon is advanced addition flow is brought into the column when the carbon is being sent to. This additional flow causes increased fluidization. The flaired column keep the carbon within the column better than a straight sided tank
As can be seen with the flaired columns, the long- lived anode, the knitted mesh and the versatile Fourth generation E-cell, Scotia continues to work for advancement of the gold recovery technology. Scotia is always looking at the various aspects of gold recovery and continues to work to advance the technology to show there are difference in the equipment and the suppliers.