Gravity Separation & Concentration Methods

Gravity Separation & Concentration Methods 2017-03-23T09:48:57+00:00
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Best Gold Wash Plant (20 replies)

Carmen Ibanz
1 year ago
Carmen Ibanz 1 year ago

I am mining in Ghana and wonder which type of gold washing plant are better: rotary scrubber/ trommel or drum scrubber/ trommel concentrator.

Carl Jenkins
1 year ago
Carl Jenkins 1 year ago

The source of the equipment may be less important than making sure you have the right equipment and that it has the capacity for your operation. Also making sure that you have the correct type of equipment for your operation, do you need any crushing and screening, what type of separating equipment do you need, and similar. After that check what others in the area are using and how successful they are with it.

There are many companies around the world making modular/mobile wash plants with an emphasis on processing alluvial material for gold, diamonds, and other material. They have been used for a fairly long time, very successfully. Lately several Chinese companies have been copying these and selling them in markets such as Central Africa. These plants have several different circuits possible, each suitable to a particular type of material. Most often they are Primary crushing followed by a trommel then to a primary jig followed by a secondary jig with a sluice on the tails.

If you are looking for information on a particular plant the best source is always the company that made it. If you are looking for general information on gravity separation (jigs, tables, spirals, sluices, and such) take a look here:http://www.smartdogmining.com

Bill Rico
1 year ago
Bill Rico 1 year ago

Depends on the particle size distribution and mineral make-up of the alluvial/eluvial/colluvial/ Colluvium gold ore you are processing. If there is a high clay/silt content and the moisture content is just right, which would be more common in low energy, tropically weathered surficial systems in West Africa, Guyana, Brazil etc., then you would need to scrub the ore prior to screening and gold recovery. If the material has very little clay/silt content making the ore loose and "free washing" such as the gravels making up the gold placers in the Yukon and in Russia, then you probably don't need to use a scrubber and could use a "wash-plant" based around a screen mechanism such as a screen deck or a trommel screen. Don't make the mistake of confusing a "trommel" with a "scrubber". The two are not the same thing and do entirely different work.

Dizzy Flores
1 year ago
Dizzy Flores 1 year ago

I worked in West Africa for a number of years mining gold and diamonds and the plant we designed initially wouldn't retain the fine gold so I had to put in side sluice boxes into the circuit-it’s always wise to find out these physical parameters before ordering an expensive washing plant that may not do the job you think it will, especially when you likely have to pay up front for any manufactured plant fem offshore sources (i.e. the Chinese model you are describing) we had great succession using Denver Jigs and a small gravity fed lab model for fine cleanups -I even resorted to hand panning to concentrate and winnow out the black sands(Fe)- in Alaska sluicing was entirely different, as we had to get rid of the rocks, cobbles etc. in order to retain the fines and flake gold- almost no clay there to bother us but oils were an issue(salmon) as it coated the gold flakes and didn't allow them to sink into the riffles for final retention - you learn these things as you observe/ gain experience in the different systems.

Carmen Ibanz
1 year ago
Carmen Ibanz 1 year ago

Thank you very much, be sure to take a look. The use of trommel seemed more difficult (repair). China washing plant is easier. It is important in Africa.

Ace Levy
1 year ago
Ace Levy 1 year ago

I am also into the small scale alluvial mining in Ghana and from experience i will say the use of the locally made wash plant is much faster than the scrubber or trommel.

In terms of recovery the latter is best but there is this trial i did and that is a plus to the operation.

The sump product that is handled by the gravel pump is sent to the wash trommel and the escaping gold is trapped by the use of sluice box and mat arrangement.

Zander Barcalow
1 year ago
Zander Barcalow 1 year ago

All advices above are very useful with great experience. Before investing in equipment’s I suggest you take some good samples of what you're going to exploit - send it to a good lab and characterize your ore, best processing route, details like necessity of milling (and what size) - ultimately how you can do the best with the lowest investment - "flight plan" avoids crash.

Marshal Meru
1 year ago
Marshal Meru 1 year ago

For my experience you need to split your method, free mercury, of course, with scrubber, vibrating screens, jigs, concentrators and shaker tables. You should to consider the fractions of gold 2 mm for coarse gold. I don't recommends sluice box for a security matter. You should consider to doing your gold separation in a "Gold room" where you will set up your concentrator and your shaker table. I'm doing that process in Guyana with a good results.

Carmen Ibanz
1 year ago
Carmen Ibanz 1 year ago

We tried to use a scrubber-butare with the sluice and the concentration table. It was not effective. Scrubber-butare could not wash more than 100 buckets gravel per day. China washing plant could wash nearly 300 buckets per day. Next. Concentration table takes a lot of time, electricity and service. Manual debugging on a small sluice is much faster, easy in almost the same efficiency. As a result, we stop to use of the concentration table and scrubber-burare. Experience with a more powerful scrubber-Butare was not. As I said before, I believe that the simpler the better equipment for Africa. Because the service is slow and spare parts are not very good quality. Site don't have to stay.

Marshal Dienes
1 year ago
Marshal Dienes 1 year ago

The Chinese make excellent scrubbers! We are experts with conventional and Chinese equipment. To be truthful, you cannot beat Chinese plant - but there are a few tricks in operating it efficiently and securely, which even the Chinese do not know!

Sugar Watkins
1 year ago
Sugar Watkins 1 year ago

When talking about mineral processing plants sorry but it looks like you are generalizing and my opinion is both South Africa and Russia still have cutting edge technology and even we in Brazil we still have our place to be considered. We know that, via standard, China use to copy a little bit of everything from a few decades ago and do not have such a tradition considered in mining, and so I believe their equipment for this branch must have been copied as well. So in this case I think it's not right assign to them the merits. Their products may be cheaper and the reason of course we all know, but put their technology in mining equipment as the best there would be an injustice and naive.

Carmen Ibanz
1 year ago
Carmen Ibanz 1 year ago

I agree with you completely. It is real picture in mining in my experience. I understand that worlds technology go forward every time and not Chinese technology. Here I am not talking about what is the best equipment for mining. Just question what are better for alluvial in Africa - trommel or Chinese washing plant.

Zander Barcalow
1 year ago
Zander Barcalow 1 year ago

When was the last time you bought Chinese equipment? Brazilian! Especially pumps and centrifugal separators. Fair prices too. But generally Brazilian marketing is poor and Portuguese language is an issue for many. I have bought/commissioned/used extensively.

DO NOT ASK THE CHINESE TO DESIGN A PLANT - But if you KNOW what they supply and you can design your own configuration and take care of security issues - THEY CANNOT BE BEATEN. However modifications and care must be taken! Don't just expect to order over the internet, you have to go and talk to them - that is their culture. If you pay a bit extra - you will get MUCH MORE from them. Another example is conveyor belt. If you go direct to a factory in China, you will get BETTER quality than anywhere else! It is just that intermediary trading companies and agents outside of China want their cut. This pressurises the Chinese into cutting corners, lowering quality and costs in manufacture. Talk to the factories - THEY DO NOT WANT TO DO THIS, but are driven to do so! For gravity separation plant, unfortunately South Africa cannot compete (though the equipment is good) - South Africa does not really manufactures jigs. It is just that the industry considers S African equipment as the standard, so for the time being - they are still selling, but this will die out if they cannot change. For example for diamonds, DMS plant (almost entirely manufactured in South Africa) is totally unnecessary, overpriced, high operating cost and over-complicated, but is taken as standard. Because the world wants to conform with the Stock Exchange normalities and still do not know what is available in China, nor know how to deal with the Chinese, they buy South African. In 5-7 years’ time things will have changed. The industry is presently plunged into depression - WE HAVE TO LOOK TO CUT COSTS - Operational and CAPEX. Even now, jobs are getting short, mines are closing.

Bill Rico
1 year ago
Bill Rico 1 year ago

As there is still no intimacy between us, I believe you used this term considering my age and perhaps also the 44 years of experience in the mineral processing branch, but just to you know, I'm still on active work with some done recently in several countries as for example in Canada where I attended the assembly and supervision of plants to evaluate Victor pipe and others currently in production in this country, and here in Brazil such as the Braúnas pipes of Lipari Mining which evaluation was a success.

As you said above, the Chinese experience is not enough to ask them to design a complete processing plant and they can manufacture it. You have to know what you want and make it clear to them what you need.

Some examples I have seen lead me believe that the quality is not so magnificent.

As for DMS for diamonds do you know any one more efficient equipment? What DMS components are not produced in South Africa? Of course I am not referring to the DMS backyard manufacturers as I know some in South Africa but yes equal to the Bond, ADP Metco etc.

What about Flow Sort, is there also any more efficient machine?

Contrary to what you said, the DMS operation is not so complicated, as it was not so hard for me to train several operators in Canada, Angola and Brazil. About to look to cut costs, I fully agree that nowadays we have to worry! According to your comment it sounds like you've been in China, could you please give us an overview of the situation and conditions imposed on its employees that enable China to provide equipment and machines more affordable? What can you say about their salaries, personal safety of workers and other labor rights? From what is said in Brazil is still a system of slavery, is it true? If that is true, in your opinion is it just and fair to support and finance this system? 

Jean Rasczak
1 year ago
Jean Rasczak 1 year ago

What examples have you seen of Chinese equipment and where/when?

I have worked on and installed more than 20 DMS plants in my career with De Beers, Trans Hex & several others. From the Bateman's to the Bonds to the River Diamonds to the DRA's and the 'back-yarders'. There is nothing you can tell me about DMS. It is CAPEX intensive, power intensive and labour intensive compared to simple jigs and new Chinese gravity separation devices. When a cyclone feed pump starts to play tricks, you can be in serious trouble with delays, and with clay build-up in circuit, and you can achieve the 'inversion affect', where there is NO separation at all.

THERE IS RARELY A NEED TO USE DMS - if you know Chinese equipment, even in large scale static plants and down to 0.5mm. There is far less limitation on top cut-off size with jigs. Smaller DMS modules can only go to 8, maybe 12 mm maximum.

I gave some examples of the issues around Chinese suppliers. I assure you they CAN and do supply good quality equipment, at a low price. There are several companies in China you should visit. You will be surprised concerning conditions and worker motivation and satisfaction. Brazil too (especially vertical centrifugal separators & pumps, gravel and water). I think Brazil is advancing well from what I saw 3 years ago.

Perhaps my ethics/knowledge of country politics are not well developed, but if there is a product at a good price, I am a project evaluator and technical Geo-Engineer, and think FIRST of my clients profit or loss. If by changing extraction and process methods, I can make a project successful, why should I consider political environments and personal safety of workers and other labour rights?

Flow sort - fine, but expensive and delicate, I would rather see a grease system with intense security if I am not near South Africa.

Ace Levy
1 year ago
Ace Levy 1 year ago

What is more efficient than a DMS or flow sort? But - remembering this is a time to cut costs. Decisions about what to use depends upon where we want to go.

Accuracy/efficiency / low costs / old ideas to reduce volumes (of gravel) that permit us using new technologies as flow sort - everything depends an accurate study for decision.

Dizzy Flores
1 year ago
Dizzy Flores 1 year ago

For final concentration ALWAYS try (light milling) and grease first. Cost = $10,000. I have worked on high capacity diamond mines where this is enough and not XRM's needed. Let me divulge the secret. High capacity, tipping vibrating sluices from China replace DMS completely from 0.5 - 16mm. First pass EVERYTHING, unscreened through JT-X Chinese jigs. Screen aperture size, 4 - 6mm. The next secret I will not divulge unless you take me to a project - SECURITY - concentrate removal techniques from vibrating sluices and jigs.

Jean Rasczak
1 year ago
Jean Rasczak 1 year ago

I 've had incredible results with vibrating sluices, but jigs...I'm not so keen with.

My opinion - in sediments - DMS is the worst method applicable to Kb's...

I'd prefer washing/scrubbing/ selecting by size and concentrate by any other method (cheaper) and sorting... or by grease or by XRM - but this decision is economic only. The matter is security management in several plants - grease table exposes too much.

Other question - Is the recovering of the big ones and here they are commonly findable

Carl Jenkins
1 year ago
Carl Jenkins 1 year ago

Of course, the main objective of all these discussions are always the exchange of ideas and experiences. The jigs you relates are the old known PanAm that actually, between all the various systems available, is still the least worst, and the worst for me is the trapezoidal, which were also invented in California and designed for heavier minerals such as gold etc.

In my opinion, the Chinese guys still have something to learn in this field such as in the case of PanAm as you can see there is no a slope between the cells which eventually causes an undesirable reflux and also the rifles design could be improved.

In their advertising they say this jigs are suitable for roughing and de-sliming? Since when a jig is a desliming equipment? And they say also it is a High Capacity machine? In the case of the second cell of Pan Am cannot be seen as a production cell, but yes as a security supplement and so in reality, for example, the capacity of a JT4-2A it is 9.12 T / hr, or be, 4 t / h per square meter cell, 4 x 2,28 m2 = 9,12T / Hr and not 18 or 20 T/hr as they said.

For me another error is the concentrate on the hutch! To use this system you need a density layer bed at or below the diamond density, however, this is a system that is not used any more, there is for example the inclined bed system and automatic periodic extraction that is more practical and efficient.

Another topic is the water consumption as they say 1 to 2 m3 / hr? From where they got this calculation? To date the most efficient system known to determine the right amount of water and pressure is the sensitivity of the plant operator's hand, but I can guarantee that consumption is much higher if you want to have an efficient fluidization of you gravel.

The light milling you refers is based on the calculation of 45-50% of the critical speed of the drum, but we must be careful to create a pulp and depending on the region such as Juína if there is no care you can break all your Diamonds. A few years ago we did tests there and following these parameters we were successfully.

Well, I think Flow Sort is not so expensive because at the acquisition some spare parts are provided by the manufacturer for operation of over two years. The increased wear are the frames with the beryl glass where the optical tubes photo multipliers detect the presence of diamonds and depending on the concentrate may have a greater abrasion wear, but if the energy is well established and the operator is well trained is a machine that does not give much trouble or too much maintenance, moreover in case of any eventuality the machine itself provides you a report indicating the problem. Based on the Flow Sort information and also on my own experience and the hour operating cost of this machine is about 8 zar (U $ 0.69).

I confess that I like also the grease tables, especially a model I am building, whose great efficiency is proven by some units already in operation here in Brazil. 

Zander Barcalow
1 year ago
Zander Barcalow 1 year ago

Nice research on jigs. Jigs date back way before the 49-ers though! I appreciate your design detail comments....what is an undesirable reflux? 🙁 The Chinese would gladly oblige any modifications if you were to visit the factory and one would be a fool not to visit when placing the order. They will make a place for a cow to sit too, if you wish! Jigs de-slime excellently the entire wet feed can be fed to them and there is NO need for prior size classification (which is undesirable in the case of diamonds). With some field practice on Thai and Chinese jigs, you will see what's possible in practice, real consumptions etc. for different size screen media. NO 'RAGGING' or 'density bed' as you call it IS REQUIRED! This the Chinese do not know - remember the minimum size of media aperture is 3mm - even 5mm is fine - the next stage of concentration is secondary jigs in the Chinese or Thai configurations and in my configurations - vibrating sluices - super simple super cheap. But how to move concentrate from the jig beds securely? This is a massive issue with factory units - but easily solved.

Marshal Meru
1 year ago
Marshal Meru 1 year ago

In jigs we call reflux the interference of the suction cycle of a cell in the expulsion of the other cell. To avoid this effect we use a level difference between the two cells of 2” or 3” and another gain is because it generate a slight waterfall, which also helps the concentration of the 2nd cell.

In the assembly of a project with jigs, I do not like to put them in sequence, ie primary and secondary, because with this system the loss of diamonds below 5mm is proven to be big. So I prefer to set them in parallel, making a size classification on 2 sizes, i.e. 8mm. A classification in more sizes also I do not advise, because the larger particle will have big interstitial spaces and in this case it loses much the effect of jigging, where often the operators to compensate, use erroneously to increase the amplitude and so having considerable loss of big diamonds.

About DMS, with a good DMC (De Beers) is easy to calibrate the density of the pulp, but no doubt it is an expensive operating cost of equipment (in Brazil we do not have good FeSi, we need to import from South Africa or Canada) and also for small mines it has the disadvantage of the particle size limit due to the diameter of the cyclone where the maximum particle size is generally: (5 - 8 Tons/Hr 18mm; 20 Tons 20mm, 50 Tons 32mm, 150 Tons 42mm and 200 Tons 51mm). Changing the inlet these limits can be increased by about 2mm but is still very limited, meaning for operation in Brazil we would have to opt for a 150-200 T / Hr DMS as in some areas big stones are very often found.

For small mines until 25 T/hr I still prefer the Rotary Pan, low operating cost, little consumption of water and electricity, very low maintenance. I am building these machines 8 feet diameter here in Brazil with some modifications and the results have been excellent. Soon, if you want, I can send you some pictures of them. 

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