Gold plants normally apply one of the following treatments to recover gold from gravity concentrate:

Intensive leach using a dedicated reactor followed by EW;
Gravity cleaning followed by smelting;
Mercury amalgamation.

The choice of one of them depends on the mineralogy and grade of the concentrate. For a plant were intensive leach has been adopted to process the gravity concentrate I think it is important to use a dedicated reactor like (Gekko, Acacia) for smooth/secured operation and safety. Indeed the fully automated leach sequence is more efficient than what could have been achieved manually by an operator. Moreover the unit can be easily secured from thieves.

Gravity concentrate normally produce gold concentrate at about 0.5 - 1 % of gold therefore usually need additional treatment before smelting. If direct smelting of the concentrate it will be pretty huge amount of concentrate and big effort for the refining. I think you are more and more experience than me. 🙂

If the ore is ground in cyanide solution, the fine gold is dissolved. The gravity concentrator then becomes a high intensity reactor. Any coarse gold captured and not dissolved could go to a table for final recovery. But one should have an idea of the amount of free gold and an estimate of the size distribution. Why spend the money for a fancy bottle roll when the Falcon or Knelson can be your reactor?

I have centrifugal concentrators in my plant that produced about 30% of total gold. The gravity concentrates contain 0.2-0.4% Au then treated either through shaking table or Intensive Leach reactor. The shaking table upgrade the concentrate up to 60-75% Au prior smelting. My concern is time to operate shaking table just only 3 hour compare 2 days when I proceed through intensive leach followed by EW.

The intensive leach reactors have a number of advantages over gravity concentration such as tables, especially in a large operation. They tend to have a higher capacity than tables, allowing for a higher mass recovery from the primary gravity extraction system, and they generally increase the overall recovery of metal from partially liberated particles which may be rejected from a gravity process. I think the most significant advantages are the security aspects. The system can in most cases be designed to minimise operator interactions and reduce opportunity for access to gold bearing material, especially since the product is a pregnant eluate which can be sent directly to electrowinning instead of being required to be treated in the gold room. The decision to go either way depends on the unique mineralogy, size and objectives of each operation.

I would also say that a two day leach cycle sounds rather long. There may be opportunity to reduce the cycle time by investigating the leaching conditions. Many reactors use a leach cycle time of less than 24 hours.

I am concerned about you are spending 2 days for an intensive leach plus EW? I believe you must to contact someone to assist you and perform some test to improve time! I do not know what kind of mineral you concentrate, but I believe 48hr is too much time! Depending of what kind of leach technology and ore this process could drop up to 6hr, 9hr, 12hr, obviously, it's depends of your ore. If you achieve 93% Au recovery in 12hr, you could leach 4 batches in 48hr!

The traditional reason that intensive cyanide leaching on gravity gold concentrates is conducted is about managing security i.e. theft. While intensive leaching has its advantages, for example the gold enters the same soluble gold recovery stream as the CIL/CIP gold and more consistent 'quality' Dore is produced, smelting is a reasonable route however does typically require a larger furnace, more fluxes and if sulphides are present, a more elaborate fume capture and scrubbing system.

The solution from an intensive reactor is typically added to the first tank with carbon, so the overall gold recovery time is dependent upon how often loaded carbon is recovered for elution. Two days does sound a long time however I guess that you may be including the elution time, with eluting probably only occurring every two days.

If there is more than 24 hours of intensive leaching time, then perhaps the leaching conditions need to be optimised e.g. higher DO, more cyanide, etc. or perhaps a regrind before intensive leaching (coarse gold would be flattened (greater surface area), while the surfaces of composited gold (e.g. between pyrite crystals) would be made more accessible, allowing faster dissolution). Smelting 65-70% gold concentrates should be quite straightforward and should not take much time.

Depending on the Mineralogy of the ore! Try shaking table optimization test. If there is enough nuggets, estimate the cost of direct smelting against the intensive cyanidation. Also estimate the time with purity duration for your final product.

You will be running longer hours because of the nature of the gold grain, shape and size. When there is nugget effect, practically the leaching time increases. It can be shorten when the reagent (cyanide), is changed over specified period of time.

Depending on the ore, additional stages of gravity processing or flotation can also be used. There are advantages and disadvantages to both approaches. All gravity or gravity with flotation or even gravity followed by conventional leaching takes space resulting in physically larger plants. The intensive cyanide leach is smaller and more compact, but like any high intensity process subject to upsets from minor process changes. A detailed comparison should be done with test work before a commitment one way or the other is made.

Thanks for your comments. I am comparing between intensive cyanide leach and shaking table.

You might want to also look at spirals and centrifuges, and do not forget flotation.

Your answer is you'll achieve higher recovery using Acacia reactor + E.W. vs. Shaking table + Induction Furnace. 98% for Acacia reactor and 99% for E.W. In other words, more gold goes into the acacia than goes on the table although the Au assays are higher for the shaking table conc. compared to centrifugal concentrator conc. but since the mass of shaking table conc. is smaller there'll be less gold going into the induction furnace. The tailing of the shaking table also comes back to the circuit again which might add to the complexity. Acacia reactor + E.W have has proven to be a robust process. The best way would be using real numbers that you get in the plant and comparing them. Those numbers don't lie they're solid.

All depends of metallurgy assays. You can do a series of leaching test. Example: Carbon in leach, carbon in column, carbon in pulp, vat leaching, intensive leaching. All depends of the grade o law of your concentrate and the mineral that you are processing. In general, intensive leach has bigger recoveries but you have to know, like I said, kind of mineral, grade of metal, granulometry. You have to do, I recommend, a trial of assays.

You will always lose gold to tails using a shaking table; this would be coarse visible gold. Intensive leaching like an ILR are perfect for leaching the tails of any of your gravity gold processes as well as full on concentrate from any gravity concentrator. Usually returns are very good-worth the cost if enough concentrate is leached. Also the resultant bar is much cleaner and purer.

Is the ore milled in cyanide solution? What percent of the recovery of gold is contained in the gravity concentrate? Any idea of the size distribution!

Intensive cyanide leaching is a great way of removing temptation so is a good security measure. Like any other section of your flow it will require constant monitoring and cleaning, maintenance etc or you will lose any advantage.

Depending on the type of coarse gold you have tables are efficient as well but require extra people and double handling of concentrates. Both need experienced people involved to set up and operate.

Your first and biggest gold trap are your Mills, bed them in and keep your densities up to give the concentrators the best opportunity.

Gold deportment across the table is really dependent on the form the gold takes and how skilled your operators are. It is pretty difficult to get a decent balance, but work I did many years ago indicated that you could expect between 60 and 70 % gold recovery with skilled operators. A poor set-up can drop this considerably; careful thought needs to go into circuit design.

I don't think that there is much argument that ICL will give you higher recoveries for the same mineralogy. As noted, you also reduce your complement, and reduce some security issues.

Generally the only times one would consider gravity over ICL is when you are not in a position to use cyanide, your gold grade is high enough to calcine and then direct smelt as noted by Grant, and I have also had clients decline to use ICL in copper-gold deposits due to concerns over the high cyanide consumption, which is an issue that really needs testing. Ores containing preg robbers also need testing.

There is usually a fairly compelling economic argument for the use of ICL over other technologies, however to echo - you will need to run the numbers and consider any other factors (usually environmental) for your case.

What specific aspects are you struggling with? I have found the vendors for the two most popular systems to be very helpful in the past, and they may be able to assist with specific problems associated with your ICL, albeit at a cost.

The following assumes you have a gold recovery to concentrate of +30%

I did a six sigma project on increasing gold recovery at a mine site recently which required me to spend a year studying the intensive leaching, gravity concentration, and leach (CIP) circuit. At the conclusion of the project we increased recovery and identified several operational problems that were not readily apparent.

The intensive leach was proven to increase recovery, as we could see tailings going up immediately after problems in the intensive leach reactor.

Gravity concentrator (Wilfley/Gemini/gold cone) produce a smeltable concentrate but are intensive to use and you need to justify the use of them versus the effort to get the gold out.

Tabling BEFORE the reactor removes coarse gold that the reactor might not recover, and the reactor leaches the fine gold that the table misses.

Gold in steel scats is more significant than you might think this Remove the iron AFTER the intensive leach, when the gold has been dissolved.

Circuit stability is extremely important and there are many variables we discovered that influence recovery and are not immediately obvious, so get out your buckets, stopwatch and start taking samples.

Your objective should bear in mind:

Any gold you recover from the intensive leach is "in the bank".

You cannot lose it down the train through solution losses, inactive carbon, on fine carbon, or in the form of process problems.

We seem to be bouncing around the original question.

You have concentrates, no matter if you use tables or Acacia, the question is not setting up concentrators or how to recover concentrates. The concentrate grades for example are the same for acacia and tables, right.

You can certainly use tables and smelt tails during a cleanup or use the calcine oven, some return the tails to the mill. If you have problems with carbon loadings, that's a different issue.

In the Leach unit, you will need to monitor the settings, people seem to play and upset the recovery. Flush/cleaning pressure needs to be higher than cyanide step or you will get sludge in your preg tank. Clean solution injectors daily if possible to ensure uniform solution throughput., and of course stay within reagent parameters, timing etc., you can do a sample campaign as mentioned, gravity/coarse gold can be patchy so what works today might change tomorrow this varies mine to mine. The Acacia tails should also return to the mill.

As mentioned vendors are approachable and will assist most times.

One piece of advice mate! Read the manual, Specs, operating procedures and maintenance.

Too many people will say I know these machines, models and strategies change. So get familiar with your make and models specs and capabilities. 95% of questions will be answered in the Manual.

All the comments you have received are good, however please try the following and you may be surprised. Run five pounds through a splitter to get a good sample. Take a pound and re-grind to 250 mesh minus. Treat with 20% HCl for 12 to 24 hours at 90 to 125 F. A lot of the iron and base metal will go into the solution. It will also release additional values that were coated with (mostly) iron and/or manganese. You have reduced the total weight of solids and freed up additional values. The cyanide would take days to penetrate the iron or maybe not at all, if a solid coating. You will also see that you can recover additional values that were hidden by the iron like iridium, osmiridium and platinum. In operations in Costa Rica, Mali and the Philippines this method improved the gold recovery by as much as 20%. I will give you one example out of Costa Rica. After all visual gold was removed we conducted this test and recovered an additional 50 ounces of gold and 40 ounces of platinum back to ton of concentrate weight. Good luck no matter what you try. There are always options but you need to find the one that works on your ore.