Hydrometallurgy: Leaching in Heap, Vat, CIL, CIP, Merrill–Crowe, SX Solvent Extraction

Hydrometallurgy: Leaching in Heap, Vat, CIL, CIP, Merrill–Crowe, SX Solvent Extraction 2017-03-23T09:50:58+00:00
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Diagnostic leaching and Gold deportment (15 replies)

Bill Fraser
1 year ago
Bill Fraser 1 year ago

I have some questions about diagnostic leaching.

Should we compare the diagnostic leaching results with Gold deportment information from mineralogical analysis? These two results should be interpreted separately or they should agree with each other somehow. Usually how much gold may dissolve in H2SO4 and HCl leaching solution? 

Carmen Ibanz
1 year ago
Carmen Ibanz 1 year ago

Diagnostic Leaching is an option taken to realize high recoveries after the conventional leaching process does not yield the required results and thus conduct diagnostic leaching to finger - print the gold dissolution phases. Gold deportment is also confirmed as a result of almost poor recoveries via the conventional leaching process and this prompts the ranking of the gold dissolution phases and at each stage realizing dissolution by a particular lixiviant and the residue can be assayed to confirm further outstanding phases of gold dissolution. I greatly feel that there is need to compare the diagnostic leaching results with the Gold deportment information from mineralogical analysis so that we can confidently finger - print the gold associations and hence confirm the poor or low recoveries by conventional leaching process or the anomalies in reagents consumptions as result of the non-free leaching characteristics of such ore type.

Victor Bergman
1 year ago
Victor Bergman 1 year ago

But if HCL AND H2SO4? I still doubt should not be HCl and HNO3 that is a total leaching.

Oberstorm
1 year ago
Oberstorm 1 year ago

Diagnostic leaching and gold deportment study are two different methods and approaches in gold metallurgy. The results acquired from the two methods should be interpreted separately but should agree with each other in certain aspects.

Firstly, diagnostic leaching is a technique commonly used to quantify gold associated with different minerals but it does not provide all the information required for gold metallurgy (such as gold speciation and grain size). Gold deportment study is a predictive and trouble-shooting tool, it not only provides information required for process selection and flowsheet development but also explains “why” or “why not” often required by metallurgists. Gold deportment is particularly useful for process optimization. Actually, diagnostic leaching is often used to confirm the amount of gold associated with different minerals determined in a gold deportment study.

Secondly, the amount of gold that may be dissolved in a diagnostic leaching test is mainly determined by gold deportment in a particular ore. The concentration and speciation of gold in host minerals, the content of host minerals and the grain size of host minerals are main factors that affect diagnostic leaching.

Alan Carter
1 year ago
Alan Carter 1 year ago

Right on the money! What method/tools do you propose using for the gold deportment? Micro-probe, MLA - Gold Search etc. There are also differing methods for diagnostic leaching, for example some people advocate fire assay as a final step for gold locked in silica whereas others advocate HF leach and then assay of final residue. It depends on which step of processing you are in as to which diagnostic leach you carry out.

Bob Mathias
1 year ago
Bob Mathias 1 year ago

For example:
We have a gold ore with significant silver contents where refractoriness is induced by the dissemination and encapsulation of very fine particles of gold and silver, primarily in carbonates, oxides and sulfides and silicates in lesser proportion.

Using the methodology of diagnostic leaching is possible to appreciate how the values are released gold and silver as it is destroying each of the carrier phases of precious metals so that the recovery will increase.

For this mineral, used first CN, then HCl + CN, then CN + H2SO4 after FeCl3 + HCl + CN, then CN + HNO3, then HF + CN. The largest recovery was obtained with cyanide and to a lesser extent with the other solutions.

Oberstorm
1 year ago
Oberstorm 1 year ago

For gold deportment study, I always recommend use a comprehensive approach involving a number of advanced and conventional techniques, including microprobe and MLA as you mentioned. Gold may occur in one to three forms in an ore or mill product: microscopic gold, submicroscopic gold and surface-bound gold, and we need to use different techniques to characterize/quantify different forms of gold. Compared to any other single technique, the advantage of using such a comprehensive approach is that a large sample will be studied to get better statistics and each issue will be addressed properly using specific techniques.

I agree with your comments on diagnostic leaching. Diagnostic leaching is indeed an effective way to determine the gold associated with other minerals. What we need to keep in mind is that diagnostic leaching is actually a “liberation” process and the information acquired from a diagnostic leaching test may be not sufficient for the project. If gold is coarse grained or if it occurs as slow-leaching minerals like gold tellurides, it may not be effectively recovered in the cyanidation after diagnostic leaching. Deportment study is the best way to obtain the information on gold extractability. Deportment study is also important for silver extraction because some common silver minerals are refractory under standard leaching conditions even they are fully liberated.

Bill Fraser
1 year ago
Bill Fraser 1 year ago

It should be better to get both information to understand gold extractability! However, I found at least in some circumstances, these two analyses may be way too different, for instance, in the present of high preg-robbing material.

Oberstorm
1 year ago
Oberstorm 1 year ago

A minor difference between the two analyses is common and acceptable. If the results are “way too different”, it may indicate that something was not done correctly. Gold deportment study, particularly for an ore containing highly preg-robbing material, can be very complicated and there are several things that may induce the errors. For example, although instrument can provide accurate analysis for submicroscopic gold and surface gold, but sample selection, preparation and grain counting of gold carriers has to be done manually by mineralogist under microscope in order to calculate the average gold concentration – that requires a lot of practice and experience. If anything of the testwork was not done correctly, a modest or even significant error will be induced. Check your testwork procedures and you may find out why the two analyses are way too different.

Paul Morrow
1 year ago
Paul Morrow 1 year ago

Diagnostic leaches should be designed for the ore. If you are worried about gold dissolved in sulphides, then you need to attack them. If you want to differentiate between gold in silica VS magnetite then you need to address that differently. We typically get better info from a good diagnostic leach than from mineralogy, as the sampling errors are much less. If you run a bottle roll with 2 kg at P80 53 µm then you have a lot of particles in the test. If you run the same samples through mineralogy you will lose a lot to fines and even QemSCAN or MLA will only test a few thousand particles. Good luck in finding the gold unless it's concentrated first. If it's concentrated first then you're not testing the whole sample. Gold not leached at all by either sulphuric or hydrochloric acid.

Gruppen
1 year ago
Gruppen 1 year ago

Both techniques are valuable and provide different, but useful, information. You are correct about the pitfalls of QEMScan but the gold association, once the grains are found, is very useful. If concentration is required first, resultant gold association and grain size data is important, even though the entire sample is not analyzed.

Oberstorm
1 year ago
Oberstorm 1 year ago

Glad to see comments from metallurgist colleagues and thank you all for your appreciation of both methodologies. As an information exchange, I would like to make some additional comments on these two methodologies.

We do diagnostic leaching tests on both ores and tailings. For new projects, it can be conducted on ores and/or tailings; and for operating plants, it is often conducted on tailings because the focus here is mainly on locating and quantifying the lost gold.

As mentioned earlier, gold deportment study is more complicated and involves a number of techniques. Errors can be induced from both manual work and instrument analysis. When use instrument analysis, pre-examination and instrument set up are extremely important. Technically, instrument can identify fine-grained gold (and silver or PGM) particles (<1µm) at high magnifications. However, for cost and turnaround time reasons, some labs may use lower magnification for gold scan (to speed up the search) in which case fine gold can be missed. Another issue that may cause fine gold particles unidentified is the preparation of polished sections (PS). If the PS is not well potted or if it is over polished (these two are common issues!), fine gold particles may not show up or can be easily polished away. If this happens, the chance of finding fine gold particles will be much lower. Another limitation for gold search using instrument analysis is that if the sample contains galena or other Pb-bearing minerals, the search speed will be much lower which may force the lab/technician to reduce the scanning area/time and therefore reduce the grain statistics and overall data quality. To avoid the above issues, a better way is to do gold search under microscope. Of course, you will need to have an experienced mineralogist with excellent microscopic skills if you want to do so (unfortunately it is difficult to find an experienced microscopist these days).

At JZMIN, we use a comprehensive approach for gold deportment study. We often do pre-concentration on a large sample and we study each of the gravity products (conc, sulf, mid, tails and slimes) to cover all possible associations. The main deliverables include speciation and estimation of liberated gold (gravity recoverable), gold associated with sulfide (floatable) and gold associated with non-sulfide gangue (finer grinding is required otherwise gold will be lost). For gold associated with sulfide, we also quantify microscopic gold and submicroscopic gold individually if it is required. Using our procedure, a number of mineralogical factors affecting gold extraction will also be identified. 

Marshal Dienes
1 year ago
Marshal Dienes 1 year ago

The approaches are complimentary as quantitative information by mineralogical analysis is too expensive - diagnostic leaching provides quantitative information while mineralogical analysis provides the qualitative information on the forms of gold and which forms are dissolved with each particular diagnostic leach.

Bill Rico
1 year ago
Bill Rico 1 year ago

In aqueous solution HCl can provide a ligand for gold and H2SO4 will provide an oxidizing agent. With HCl the gold is +3 hence AuCl4(-1). Because it is aqueous solution, it will be 2H[AuCl4]. H2SO4 does not provide any ligands. Using reaction constants may be able to calculate the amount of gold to be dissolved and how fast.

Marshal Dienes
1 year ago
Marshal Dienes 1 year ago

You need a strong oxidant to dissolve gold in acid solutions. For diagnostic leach the acid conditions can be weak or mild to selectively breaking down minerals that contain/encapsulate gold, which needs to be followed by cyanide leach to quantify the gold released. Depending on the oxidation strength and ability of the acid to leach gold, the acid solution may need to also be analyzed for gold. For aqua regia gold is dissolved and is quantified by analysis of the acid solution.

Unterstarm
1 year ago
Unterstarm 1 year ago

Just sharing of previous experience, often a GRG centrifugal concentration such as Knelson or Falcon should need to be run as the first part of Diagnostic leach to catch the free Gold content. Following the GRG concentration you may run standard diagnostic protocols of the tailing and intensive leaching of the concentrate, small amount of lead catalyst such as Leachwell could be add.


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