INTRODUCTION, - DEVELOPMENT OF CLS
CLS Leach was developed by Action Mining Company over a period of four years. The company was researching a method of recovering gold from a massive high sulfide complex ore. Research brought about the first of the CLS leaches (CLS-1) in 1979, and continued developments introduced the CLS-20 series several years later. Although our Research Dept. continues to experiment with other formulas, the CLS-20 series is still the most universal non-cyanide compound for leaching ores.
Actual expenditures for original research were over $500,000. Over six thousand experiments were conducted. Similar research conducted in any commercial lab at 8 hours per days a week would have taken over six years and cost over $1,500,000.
The CLS leaching solution was Action Mining's first product, but just as important is the technology attached to this leach solution. Since CLS is different than cyanide or any other leach solution now in use, this new technology must, in some manner, be exported for the potential use of CLS. This is not an easy problem, since few people like to pay high prices for consultants. Thus it is hoped that this manual will fill a portion of the gap.
THIOUREA – All of the information found in this manual is applicable to thiourea as well as CLS. The only difference being in the recovery percentage. CLS almost always recovers 10% to 25% more gold than thiourea.
Table of Contents
Chapter 1 CLS Easy Leach ....................................................................... 1
Chapter 2 Preparation of Ores for CLS Leaching .................................. 5
Chapter 3 Concentration of Ores for CLS Leaching .............................. 11
Chapter 4 CLS Leaching ........................................................................... 19
Chapter 5 Filtering (Removing the Leach Solution from the Ore) ......... 31
Chapter 6 Recovery of Metals from CLS Leach Solution ...................... 36
Chapter 7 Testing with CLS ...................................................................... 47
Chapter 8 Breaking a Complex Ore ......................................................... 58
Chapter 9 Fire Assays ................................................................................ 69
Chapter 10 Refining Gold & Silver ........................................................... 77
Chapter 11 To Summarize ......................................................................... 85
Glossary ....................................................................................................... 92
Some Chemicals Used in Mining & Milling .............................................. 94
Chart: Activity Series of Metals ................................................................. 97
CLS Leach is an acidic leach solution with a pH (see glossary) level of 2. The pH level must be maintained throughout the leaching cycle.
The solution must be kept at a temperature below 110°F. preferably at 70°F. Some ores require a very highly concentrated solution of CLS and some ores can be leached at a very low concentration (as low as .051%). Because of the acidic nature, CLS must be used in plastic, glass, rubber or wood lined tanks.
Since CLS was developed for use with a very difficult sulfide ore it has a tendency to work on any ore that can be fire assayed. There are many complex ores around the world that have resisted cyanide as a leach solution for gold and silver but CLS has, in every case tested, been able to get the gold and much of the silver available in such ores.
CLS as a gold and silver leach was designed to leach concentrates, but that is not the best purpose to which CLS can be addressed. All ores must be evaluated after testing to determine economic feasibility for direct leaching with CLS. Many ores will not prove to be rich enough for leaching with CLS, even though it is successful when used. However, most of these ores can be first, concentrated and then leached at a very good profit. This is true even in the the case of complex, refractory, or sulfide ores that will, not work with cyanide.
CLS will leach pieces of gold 40 mesh and smaller within 8 to 12 hours. This is a definite advantage over cyanide which can take up to a week to leach 40 mesh gold. This presents a number of trade-offs between CLS and cyanide. In most cases, the CLS leaching system can be built much smaller than the cyanide system. On the other hand cyanide is a cheaper leach than CLS, costing approximately 25% less. Cyanide is often used at much lower concentration, but the cyanide system must be much more elaborate because of the poisonous factor and the environmental factor. In most instances CLS may be dumped simply by adding sodium hydroxide to the solution. The tests required for CLS dumping are much simpler. The hazard to personnel is practically non-existent. CLS is no more poisonous than lemon juice and boric acid. With cyanide a serious mistake can be made at any time.
CLS can also be sold in large quantities for about 40% less than cyanide. In this case the CLS must be ordered specially, at more than 30,000 pounds per order. This does not necessarily mean the CLS leaching will be cheaper than cyanide, since the cyanide is often used at strengths 1/4th that of CLS. Because of the smaller system size, reduced hazard to personnel, less complex system, and other various considerations, one can often afford to spend five to ten times the cost of cyanide and still remain in the same position economically.
There are some ores in which the economics just will not allow the use of CLS. Any ore that can be concentrated will usually be suitable to CLS leaching. There are a few ores that cannot be concentrated. These ores usually contain microscopic gold so fine that it will wash away with water and thus, standard concentrating methods do not work and CLS may not usually be used economically. But because of the small particle size of the gold CLS may be used in low enough concentration to make even this ore feasible.
Cyanide is a very dilute solution and is used at concentration of less than 1%, and cannot be used in greater concentrations. When cyanide is tried at higher concentrations it quits working and nothing but dilution of the solution will help. Thus a cyanide leach solution will contain limited quantities of gold per gallon of water and large amounts of liquid must be used in any operation to contain a reasonable amount of gold. The use of cyanide on concentrates requires large amounts of cyanide leach liquid for a given amount of concentrates. This may or may not be a problem. This is not a problem with CLS which can hold up to 4 ounces of gold per gallon of solution and thus many new leaching operations are possible.
The amount of gold that one gallon of full strength CLS (8, ounces of CLS powder per gallon of water) will hold in solution is approximately 4 ounces. When working with ores this figure will vary widely because of the other impurities that might go into a CLS solution. In any case, CLS will always hold at least 100 times more gold than cyanide, thus allowing much smaller amounts of liquid to be used in any given system for a given amount of ore.
Since there are a number of ways to handle any given ore with CLS one should explore each avenue carefully before adopting any particular system.
Many ores may require a simple pre-wash with water before leaching to remove the soluble minerals that interfere with the CLS process. Other ores require a pre-leach or an acid pre-leach to remove excess poisons and various metals such as lead or copper. Some ores such as clay can require a drying process before leaching to reduce or eliminate filtering problems that arise in most clays. In almost every case there is one method of treatment that will prove to be economically feasible. Although cyanide is lower in price per pound, the basic trade-offs of CLS will usually over come the cheaper price. CLS trade-offs with cyanide:
1. CLS is safer for the environment.
2. CLS is safer for personnel.
3. CLS systems are smaller.
4. CLS systems are simpler.
5. CLS will work with many ores that are not suitable to cyanide
6. CLS governmental permits when needed are faster and lower in cost.
7. CLS will handle a great deal more gold per gallon of
liquid than cyanide.
WARNING; Never mix cyanide and CLS. Extremely toxic fumes will result from the cyanide that can be fatal.
CLS is biodegradable but should be neutralized with sodium hydroxide or any other suitable chemical to pH of 7 before dumping.
PREPARATION OF ORES FOR CLS LEACHING
PREPARATION OF ORES FOR CLS LEACHING
The simplest and easiest preparation that can be done to any ore is grinding or pulverizing. That can become a somewhat complex problem in itself. These are some of the questions that could be asked about grinding ores:
1) How fine to grind?
2) What grinder to use?
3) Should one roast the ore?
4) Should one classify as to particle size?
5) What sizes should the particles be?
TESTING FOR MESH SIZE
The simplest answer to how fine an ore must be ground is this; the gold must be released so that the leach will reach the gold particles. In some ores -40 mesh will be small enough and all of the gold will have been released by the time the ore has been ground to -40 mesh. (See glossary for definition of -40 mesh). On the other hand if the gold particles are microscopic in size the ore may have to be ground to -200 mesh or even -325 mesh.
Of course, the finer an ore must be ground, the more costly the operation is going to be. The finer the grind, the more costly the machinery is going to be that does the job. In addition, finer ore is often more costly to handle.
In order to determine the maximum size to which an ore may be ground for CLS leaching, thiourea leaching, or any kind of leaching, a number of tests should be run. One can rough grind to -40 mesh or even -20 mesh and run several CLS 2 tests on 2 pounds or one ounce of ore (See Chapter 7 for test instructions). Then several tests on ore that is ground to -80
and several tests at -100 and several at -200 mesh. It may even be necessary to try several tests at -325 mesh, if each of the above tests get progressively higher recoveries.
When preparing ore ground to various mesh sizes it is okay to simply screen the ore through screens of the given mesh size that you desire. For example, all of the ore that goes through a 40 mesh screen would be considered -40 mesh.
Once the proper mesh size for leaching has been determined one must decide what kind of milling equipment will be used to do the job.
Over the past hundred years nothing has been designed that out performs the ball mill or rod mill for grinding ores. The ball mill just continues to grind ore to any mesh desired day in and day out. Once in a while one must throw in new iron balls as the old ones get ground down and maybe, once a year the liners may need changing.
There are, however, a number of cheaper ore grinding devices that can do some of the job. Some of the impact mills and hammer mills now on the market do limited jobs.
The author has never found an impact mill or hammer mill that would meet the specifications given by the manufacturer in reference to the quantity of ore handled before breakdown. But in some instances these mills will do the job that is required. When the ore to be ground is a very brittle quartz, or a dried clay, or a dried placer dirt, the hammer mill often does a good job. But when the ore is a hard quartz or a sulfide quartz or any number of other super hard ores, a hammer mill can be totally destroyed in one hour. Hammer mills are a good buy when used properly and a poor buy when used for the wrong job.
In a case where the ore is fairly soft and the hammer mill bought is one in which the hammers can be replaced readily without a lot of labor, the low cost of the hammer mill in comparison with a ball mill may more than pay for its use. In some cases the hammer mill or impact mill may just give one enough production to get the operation going. But in the long run, when grinding ore, a ball mill will pay for itself many times over, and will pay for any number of hammer mills. Many miners have bought impact mills hoping to get production under way only to find that the impact mill did not last through the first week. One should be careful to test any hammer mill or impact mill on several tons of his own ore and then remove the hammers to examine the wear.
Many impact mills and hammer mills and most ball mills can be set to produce ground ore of any size from -20 mesh to -200 mesh. The impact mill does this by recycling the larger pieces back through the mill. This process in itself causes extra wear, because the pieces that do not break up are extra hard and extra abrasive. After a while there is a large quantity of hard abrasive pieces, just a little larger than what the machine is adjusted to produce on a continuous circuit, circling around through the machine.
There are two basic variations of the ball mill so far as particle size adjustment is concerned. The self classifying ball mill is adjusted in particle size by the installation of a stainless steel screen of the particle size desired. Only those particles small enough to get through the screen leave the ball mill and continue through the mill circuit. The second variation recycles the larger pieces that leave the ball mill, back through the machine again.
ORE PREPARATION AFTER GRINDING
Many ores will require no further preparation .:.and the leaching phase may begin immediately. On the other hand, once an ore has been ground to a particular mesh size there are a number of further preparations that may have to be done. One should conduct one ounce tests or 2 pound tests without any treatment to determine feasibility. But tests must be conducted using all of the various treatments, unless testing shows a very high recovery of precious metals, above 90%.
The simplest preparation would be to wash the ore with water before leaching. Washing the ore can remove many soluble minerals, some of which may interfere with the leaching operation. One must be careful not to wash any of the gold from the ore. If the ore is to be concentrated, then washing need not be attempted, since the concentration itself will wash the ore.
Washing the ore on a large scale can be relatively simple. One way to accomplish this is to have the ore washed from the grinding mill (whether it be a ball mill or a hammer mill) into a large vat. The ore would then be removed from the vat by a de-watering process such as a large ore screw or a moving belt from the center of the vat out.
The likelihood of washing gold out of an ore is very remote. Any gold that can be seen under a 50 power microscope will still sink to the bottom of a properly prepared pond or trough. Such small gold will float if given the proper chance, but any kind of detergent in the water, even in small quantities, will prevent the floating of gold.
Many miners use a dish washing detergent such as Joy. The Amway detergent, L. O. C., is also used by many for this job. It is bio-degradable and goes further than Joy. Either detergent eliminates float gold by reducing surface tension to practically zero.
On the other hand, many desert ores carry micron gold that will wash away with the water. In that case, washing may be a method of concentration. Here is a secret to remember: any gold that is fine enough to wash away can be screened out of the ore, before the ore is wet. Of course, a lot of sand and ore will come with the gold, but it will be greatly concentrated and may be leached or amalgamated, or in some other way handled as a concentrate.
Some ores may require a pre-treatment of dilute sulfuric acid to dissolve some of those minerals that water will not dissolve, but which are coating the gold particles. Sulfuric acid can also destroy some of those minerals that have a bad effect on the CLS Leach. The concentration of sulfuric acid could be from 2 gallons of sulfuric acid (industrial strength sulfuric acid 90% or higher), per ton of ore treated, up to as high as 60 gallons.
For ores containing large amounts of copper, Action Mining has developed a relatively inexpensive copper leach. It may be necessary to remove the copper before leaching for the precious metals. The copper leach is usually used in conjunction with sulfuric acid. Although many acids will work in its place, sulfuric acid is usually the least costly and at times, may be obtained from some industrial waste companies at no cost.
There are a number of preparations that may be done to ores as a pre-CLS treatment and apre-thiourea treatment. See Chapter 8 which covers breaking a complex ore.
PRE-TREATING ORES BY ROASTING
Since roasting ores is a very well known and important method of pre-treating some ores, we have mentioned it here. However, it has been our experience that there is no advantage to roasting any ores before leaching with CLS. There may be one small exception to this rule, and that is on rare occasions it is possible to roast an ore and then wind up with a better fire assay because of the roast. In cases where a roast will actually improve the fire assay reading, it will also improve the CLS leach recovery.
CONCENTRATION OF ORES AND LEACHING
CLS, thiourea, cyanide, chlorine, bromine, and other leaches are generally used directly on ores or low grade concentrates. THESE LEACHES ARE SELDOM USED ON HIGH GRADE CONCENTRATES. Attempting to use these leaches on high grade concentrates is usually a big mistake and in the end results in a loss of money. In reference to high grade concentrates, we are talking about ores that have greater than 15 ounces of gold per ton of concentrates.
The reason that the various gold leaches are not used on high grade concentrates is that these leaches are all dilute solutions, and usually will not hold enough gold to get all of the gold out of a concentrate; but that isn't the only problem. Gold in nature, as opposed to the gold in a laboratory, has varying degrees of resistance to being dissolved by a leach. In nature it is mixed with base metals, such as iron, copper, zinc, tin, and any number of other metals. Sometimes when a leach has dissolved 1/2 the gold, it just won't dissolve any more.
Other problems with concentrates is that there will usually be larger particles of gold. Particles of gold as large as 20 mesh will take up to a week for cyanide to dissolve, and days for thiourea or CLS to dissolve. Usually the rule is, the more gold in the concentrate, the longer it takes to leach using standard leaches. Quite often, for whatever reason, standard leaches just won't get all of the gold out of high grade concentrates.
THE ANSWER TO HIGH GRADE CONCENTRATES IS TO USE EITHER AQUA REGIA OR SMELTING. Aqua Regia (3 parts hydrochloric acid, one part nitric) is generally used.
For many years small and medium-sized mining operations have sought to produce gold and gold concentrates from their
ore in as pure a state as possible. If they could produce gold metal from their tables or their sluice, they could sell the metal for a maximum profit. As they get more and more impurities into their end product the less money they can get for it. Even to this day many miners throw away good concentrates, because they can get little or no money for the sales of same.
Small and medium operations are constantly fighting to keep their equipment adjusted exactly right to produce the very best of concentrates. In many cases, if the mill operator does not have the full experience necessary to produce the highest grade of concentrates, the whole operation can fail. With a small leaching operation this need not be the case. In most cases, the mill operators can allow the machinery to be poorly adjusted; in fact this may even be desirable. With the use of CLS the mill operator can leach the entire concentrates and thus, not worry about the exact quality of the concentrates.
If the concentrates are somewhat greater in quantity (in other words less concentrated), it is of little worry to the mill operator. His leaching operation will handle the greater amount with little effort, and get as much or more gold than he would otherwise. In addition to this, if the operator is willing, he can refine his own gold and silver with just a little bit more effort and thus, increase his income at several points not available to him before.
The use of cheaper, more poorly constructed machinery may be employed successfully for concentrating, when using CLS for leaching the concentrates, rather than selling the concentrates. The machinery can be adjusted to the point where it saves the gold but still does a poor job of concentration, and CLS will still leach the concentrates.
Keep in mind that CLS will not work with many ores, but maybe thiourea, or chlorine, or a bromine leach will. In many cases even cyanide can be used.
In the past there were many ores that would respond successfully to only one type of concentration. Since CLS can work with poor concentrates, in some cases it may be more economical to use less efficient machinery and produce a less concentrated concentrate and let CLS do its thing. In any case, Action Mining Services Inc. has spent quite a bit of time and money researching various concentrating methods and machinery. We would like to point out a few of the good points and softie of the pitfalls.
A concentrating table is a table on which the ore is moved towards one end with a bumping motion of the table, while water washes the ore crosswise off the table. The theory is that the heavy pieces will not be washed away and thus, will move across the table and fall off the end, while the lighter pieces will be washed over the side.
There are a number of concentrating tables for sale on the market. Some cheaper tables sell for under $1,000.00 and some good, larger tables sell for as much as $50,000.00 and more. Naturally one gets what one pays for in concentrating tables, just as with houses or automobiles.
A concentration table is used primarily to produce concentrates. While a good table, well-adjusted, will often have a line of pure gold coming off the top when in operation, that may not be necessary. The fact that the gold is caught somewhere within the concentrates coming off the end of the table may be all that is necessary, because the CLS leach will get all the gold anyway. Thus, one could use a table that is less than the best.
When considering a concentration table, one should look for a table with a very smooth action. The table must move back and forth, and bump at one end of the motion, without any vibration or up and down motion. This takes a very heavy base and a back and forth sliding motion. Many of the cheaper tables are mounted at the end of a long leaf spring or just a flat bar of iron. These tables vibrate badly and will lose much gold in some instances, and a little gold in other instances. The really expensive tables have heavy bases and heavy table tops and they move back and forth on bearings. They do not sit on springs. Of course, they will do the best job. The cheap tables can do some jobs and they have their place, but the idea that a cheap table can be adjusted to do the job that the heavier table can do is false and has been proven false many times.
Adjusting a concentration table for proper operation is similar to swimming. You can read about it all you want, but you finally have to practice for a while before you can do it well. There are some important points that one should keep in mind.
It is important to classify the ore according to size and to run one ore size across the table at a time. If the ore has too many different mesh sizes of particles, the larger particles will interfere with the smaller particles, preventing proper operation of the table. For the most efficient operation of a table, only one mesh size should be on the table at a time. This is usually not practical, since most of the ore would have to be stored while one mesh size was being run.
On the other hand, not to classify at all almost eliminates any usefulness one might get from a concentration table. A good rule of thumb for mesh sizes on any table, would be 20 mesh to 50 mesh at one time; then 50 mesh to 80 mesh at one time; and 80 mesh and smaller at one time.
The question has been asked, "Why not just grind everything to 80 mesh and smaller, and not bother with the larger particles?". In some cases this might be okay, but in many ores there are large gold particles ranging between 20 and 80 mesh. When tabling an ore these gold particles are the easiest to separate out; but in the process of grinding to 80 mesh these gold particles will be ground into many smaller particles, making them harder to separate out, and some gold will be made small enough to wash away. Thus to some extent, the smaller an ore is ground the harder it is to handle and to concentrate. (See Chapter 8 on breaking a complex ore and for more information on determining proper mesh size for any ore.)
The tailings that are washed off a concentration........................
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