You are not supposed to mix both waters from thickeners. Zn thickener water will go to Zinc circuit only and not to ball mill or lead circuit.

It looks as though you have ruled out liberation as the cause of the zinc recovery however have you checked if the sphalerite is being recovered via entrainment rather than activation and true flotation? You should check this especially if there is a fine grind.

To check if it is ions in the water you could do some batch tests with different water sources for the makeup water. If it is recycled water do you have an analysis of what species are present? If this is the problem you can look at treating the water to complex-out the ions causing activation. Please keep in mind that the activation could also be due to dissolution of other minerals present in the ore rather than recycled water.

As suggests water source is important. Many ions can activate sphalerite, apart from the obvious copper, lead and silver are likely. A relatively simple test is to run EDTA extractions, on samples of ore, post grinding, and the lead concentrate. Look for changes in metal ion ratios. Then add the correct ion complexing reagent into grinding. Collectors add after grinding/complexing.

I completely agree with your suggestions. I'll be glad if you refer me to a downloadable reference that completely explains the entrainment in such these kinds of ores.

The first parameter we checked is the water resources. So we prepare 3 samples of ore with equivalent amount of lab grinding. After that by testing with fresh water, recycling water, and pure water, we see that a little change occurred in results (less than 2% changed for Zn in Pb conc., more than 20% Zn in Pb conc.) due to replacing kind of waters in our test. Furthermore, one obvious conclusion comes to mind that the water have less effect in this unselective flotation.

I really appreciate your suggestions, but we don't have access to EDTA extraction test. During lab grinding I add 6 gram sodium phosphate to 900 gram sample I prepared for the test. By this thought that lead tends to dissolute in water and may release Pb ions as you said. So after doing such this test the results didn't change and again we had more than 20% Zn in Pb conc. adding cyanide complex due to Cu ions also had less influence in selective flotation of Pb conc.

I agree with all the previous comments from our colleagues. Just for comments, I have been working with specific Pb-Cu-Zn minerals with highly Cu-Sphalerite activated particles that result in 17-22% Zn in the Pb concentrate; and I have managed a Pb concentrate with less than 5.5% Zn. As said, many ions can activated sphalerite, so you must use the right complexing chemical in the early stages of the plant concentrator to reduce the Cu-Sphalerite activation.

As you stated the cu-sphalerite activated will not be floated in Pb concentrate. If we complex-out Cu ions by a reagent like sodium cyanide (NaCN). But adding NaCN didn't work in such similar lab test. May you suggest the reagent you used in your plant that complex-out cu ions?

The Ag content of this ore is high and it will be a though that Ag ions would do this activation on sphalerite. If it will be true, what are the best reagents that wash-out the Ag-ions from milling pulp?

Sphalerite activation by lead ions is well known and dealt with by the addition of zinc sulphate. Entrainment is a phenomenon based on particle size compounded by froth 'stickiness'/draining capacity - and is not ore or mineral specific. The addition of a very small quantity of sodium hydrosulphide during milling will precipitate any base metal ion and prevent activation. However don't add too much.

No EDTA as a rough guide, precipitate the base metal ions out with hydroxide of say a litre of filtered slurry and assay the precipitate. 

I’ll test it but one question still remains in my mind. Your suggestion was performed with difference in type of sulphidizer (sodium sulphide) after milling operation. It has a sensible changes but not the acceptable difference it made.

Because the consequence of this production procedure leads to floating Zn sulphide and after that Pb Oxide, this question arise that May this amount of sulphidizing reagent activate the lead oxide that comes to ZnS concentrate?

As you know the leaching stages of ZnS concentrate is highly dependent on containing minerals (i.e. Galena or cerussite). Does Sodium hydrosulphide do the opposite and except of washing-out ions from pulp, do the activation on lead oxide?

The use of sodium hydrosulphide or 'sulphidiser' is about the precipitation of base metal ions at the milling stage and thus prevention of activation. The quantity should not affect downstream flotation. Although it will 'clean' any oxidised sulphide surfaces, thus improving collector efficacy.

Greater quantities of 'sulphidiser' under controlled conditions (cf. Control Potential Sulphidisation : CPS) are required to effect 'sulphidisation' of base metal 'oxide' minerals or surface oxidised base metal sulphide minerals. If base metal 'oxide' minerals are present, the normal practice is to float the sulphide minerals firstly, followed by 'sulphidisation' [or leaching] of the base metal 'oxide' minerals.

The level of sulphide/hydrosulphide ions present during the recovery of lead 'oxide' minerals by 'sulphidisation' would depress most base metal sulphides due to collector displacement. The earlier comment about 'not adding too much sulphidiser' was alluding to depression.

Hopefully these comments have addressed your questions.

My experience of lead activated sphalerite (Mt Isa, Hilton, Elura, NevesCorvo) is that soda ash (Na2CO3) added into the mill in combination with zinc sulphate and metabisulphite (MBS) to the mill, or before aeration and collector addition, can assist sphalerite depression whilst floating galena. Cyanide is not effective for lead activated sphalerite. Add soda ash (200-1000 g/t) to the mill feed to raise the pH of the mill discharge to ~9-9.5. What is the pH of the ore when grinding with only water? Add zinc sulphate (200-800 g/t) to the conditioning stage at this pH (9-9.5) which is optimum for sphalerite depression (see papers by Fornasiero et al). Add MBS (200-600 g/t) also if necessary. Once you get sphalerite under control, consider switching to a better lead and silver collector such as 3418A phosphinate collector which has benefits when using MBS. If the ore is heavily oxidised, you may need a lot of soda ash which may be detrimental, however moderate soda ash to the mill feed is good for fine galena recovery. Pulp temperature is also important for galena flotation with ethyl xanthate and MBS. Switching to 3418A may give fewer problems with temperature if that is the case (see papers by Johnson et al).

Grano, S.R., Johnson, N.W. and Ralston, J., (1997). Control of the solution interaction of metabisulphite and ethyl xanthate in the flotation of the Hilton ore of Mount Isa Mines Limited, Australia. Minerals Engineering, Vol 10 (1) pp 17-39.

In this paper, it was possible to reduce Zn recovery from 40% at 80% lead recovery in a roughing stage to less than 20% at 80% lead recovery in the roughing stage by adding soda ash to the mill with MBS added in the conditioning stages.

Grano, S.R., Ralston, J. and Johnson, N.W., (1988). Characterisation and treatment of Heavy Medium Plant slimes in the Mt. Isa Mines lead/zinc concentrator, Minerals Engineering, Vol 1 (2) pp 137-150.

In this paper, the fine fraction (slimes -100 microns) of a lead-zinc ROM ore is more oxidised and hence there was evidence for lead activated sphalerite than the coarser size fraction at Mt. Isa. At Mt. Isa they treat the "slimes fraction" of the ROM ore separately, thus avoiding lead activation of sphalerite in the ground feed. They add zinc sulphate to depress lead activated sphalerite (now with soda ash I think) in the 'slimes circuit'. The slimes circuit treats about 10-15% of the ROM ore without the need for grinding and the chemistry is tuned for this fine, oxidised, lead-activated fraction in isolation of the main stream which is ground in mills separately. Hence, there is better overall performance as the chemistry can be tuned to each stream separately.

A lot of experience is now published in journals such as Minerals Engineering and in publications such as:

Grano, S. R., (2010). Chemical measurements during plant surveys and their interpretation. Chapter 6, in Flotation Plant Optimisation: A Metallurgical Guide to Identifying and Solving Problems in Flotation Plants, (Ed: C J Greet), Spectrum Series No 16 (The Australasian Institute of Mining and Metallurgy: Melbourne). ISBN: 978 1 921522 14 7, pp. 107 – 121.

NaCN alone didn't work for a proper depression of Cu-Sphalerite particles. You must use ZnSO4+NaCN (ratio 3:1 ó higher), a combination of lime and Na2CO3 if you need to increase the pH, and MBS with aeration in the right pH range.

For entrainment a good paper is from the Centenary of Flotation Symposium in 2005. It is available free online from the AusIMM site (if you are a member) and also at OneMine. If you’re not a member you can purchase online also. Johnson, N W, 2005. A Review of Entrainment Mechanism and its Modelling in Industrial Flotation Processes, in Proceedings Centenary of Flotation Symposium, pp 487-496. (AusIMM, Melbourne).

There may be newer work that others can suggest but this one is an excellent summary and starting point.

The topic of enriching the Pb con grade and Pb recovery by (maybe I am bit elaborating the discussion domain)

Reducing the floatability of sphalerite reporting in galena floatation by reducing the effects contributing to pre activation of sphalerite ions available in ore. The selection and combination of surface chemicals like Zinc sulphate, sodium cyanide, sodium silicate, sodium carbonate, sodium hydro sulphite, hydrated lime, Meta-bisulphate and etc will play pivotal role. The combination and dosage regulation proved by test works depends on the species present in the ore and active influence on sphalerite activation needs to be regulated, tested, reviewed and confirmed in plants with sample campaigns and results.

Reducing the entrainment of slimes and fines of sphalerite reporting in galena flotation circuit can addressed for reduction in column flotation with increased froth bed with wash water facility in combination of flotation chemical. This equipment is also help full for the minerals which are having near range flotation kinematics.

The third method of using High gradient magnetic separator is also beneficial exploiting the difference in magnetic susceptibility properties of galena, sphaleriteand chalcopyrite grains. There are fine matrix carousals available depending upon the PSD of grains. A test work to confirmresults is must as usual but option is worth of cross examining.

Regarding the entrainment mechanism for Sphalerite recovery into the Pb concentrate; a simple and quickly way to investigate if the entrainment is one of the Zn (or sphalerite) mechanism for recovery is to perform a size-by-size assays and review how the Zn (or Sphalerite) is distributed into the Pb concentrate. Normally, the entrainment is most important for particles sizes below 38 microns (< 400 mesh).

There are some applications where flotation columns excel. In my opinion, based on experience of operating columns in this and other duties they don't work well in galena applications. It is possibly due to the high SG limiting froth depth (and also bubble rise velocity) but the column seems to kill off the kinetics and consequently builds up a large CL in lead circuits. The CL build up is a lot quicker than in say zinc or copper cleaner application). A wise man (mentor and boss of mine at the time) once made a comment that for lead circuits the best thing you could do to improve column performance would be to chop them in half. I think he was right! Saying this I'd be interested in hearing of your experiences with columns in lead cleaning duties.

I definitely agree with your comment on wash water helping if entrainment is the cause however for a lead flotation circuit I'd look at putting wash water on the mechanical cells to do this. We've had a lot of success fitting wash water to mechanical cells (conventional and tank) to remove entrained gangue and penalty minerals.

A lot of what has been mentioned here is applicable. In my view getting the chemistry correct is the most important step which is largely driven by the Intrinsic Iron Content of the Sphalerite you are dealing with. Low iron sphalerite exhibits quite differing flotation properties to high iron types.

Your Idea is somehow performed in a big Lead & Zinc Plant, named "Calcimin". They are Using Column cell with water above froths that gives a product with higher amount of grade rather than SALA cells. I really interested to know how to apply different treatments for flotation of iron and non-iron containing sphalerite. The different color of concentrate (brown to darken brown) in consequence of froth products, proves your statement, but how to treat?

Request to bit elaborate CL in your comment.

Agreed that flotation kinematics and froth bed level is low in Galena when compared to sphalerite and Chalcopyrite so correction to chop column height to half for better economy is very good! I have used Metso micro cell sparger columns in sphalerite and Apatite in cleaner stage for reducing entrainment and penalty minerals, but sorry not in Galena cleaners . It is also observed that galena is over grinded in pb-zn grinding circuit because of its High Sg grains and to counter this we have put flash flotation cell in hydrocyclone under flow to grab the coarse galena. We have also used Nigrosine for carbonaceous/ graphite material. NaCN, znso4, hydrated lime, sodium silicate for improving pb con grade or reducing the misplacement.

May also request you to look into the possibilities of using High gradient magnetic separators for increasing Pb Con grade or reducing misplacement. The finer matrix is effective even at 20 Micron in haematite iron ore which I have commissioned in India, but test works for ore having galena, sphalerite, chalcopyrite, pyrite, pyrrhotite, silica species and traces of arsenic, antimony, bismuth, cadmium, silver minerals needs to be carried before concluding please.

You can tell from all the comments on this topic that there isn't any hard and fast rule that applies to all ore types, so you must navigate through your particular situation armed with the advice volunteered in this discussion.

From my experience , the moderate to high iron containing sphalerites are easily depressed in lead float by floating at near neutral pH, using zinc sulphate as a depressant as well as SMBS (up to half kilo/t of each), and also using a light collector such as Ethyl-Xanthate, and MIBC frother. Good examples of zinc sulphate depression capabilities emerge from the Red Dog mine where ZnSO4 occurred naturally in pit and South Broken Hill where ZnSO4 accumulated in recycle water streams. The sphalerite can be reactivated with CuSO4 at higher pH (10) after lead float.

With the low iron, caramel\honey coloured sphalerite such as Century Zinc mine I don't have direct experience, perhaps someone else can guide you on this.

I'm glad you're getting good ideas for the effective depression of sphalerite into the Pb concentrate; and recalling your original question "What’s the suggestion for depression of such these pre-activated sphalerite that comes in Pb concentrate?” I have noticed that different topic is rising from our colleagues "iron content into sphalerite particles - Zn grade".

So, I'd be glad if you can state what is the problem you are leading with the sphalerite flotation process so I may be able to highlight some issues related to the new topic. And may be, it would be good to start a new discussion so other colleagues may be interested and made some comment as well. 

As discussed above, when using ZnSO4 for sphalerite depression, the pH needs to be above 9 to form the ZnOH species that will coat the activated sphalerite surface and stop the activated sphalerite floating.

Also in a previous discussion about a month ago, (I presume this is the same ore type that we are discussing now), we discussed using dilution cleaning test work in the laboratory to determine the amount of entrainment in the flotation test work, and you commented that you were going to conduct flotation with dilute pulp (dilution cleaning) to compare with the normal cleaning results, and determine the level of entrainment. What did you find from these results?

Sure, I'll do it to have useful information's and experiences of our knowledgeable friends in that field.

My strategy is based on 'stopping things from happening' - always better, particularly in flotation, than trying to solve the problem once it has happened.

What is causing the pre-activation - mineralogy (' base metal oxide' minerals or oxidised sulphide minerals), moderate levels of base metal species in the recycled water (cf. the early days of the Thalanga operation many moons ago)? If you can't knock these ions out into a non-activating form (e.g. sulphides), then you need to test one of the many recipes that contributors have kindly provided.

With regard to entrainment, minimise the production of fines if at all possible - which usually comes down to the classification circuit. Screens have demonstrated advantages with high SG ores. But there will always be fines, so entrainment is a reality. A variety of techniques can be used to address the issue, usually in conjunction- such as lower percent solids slurry, making the froth better draining (e.g. MIBC), deeper froths and froth washing - where columns can be useful.

When the Thalanga operation was having selectivity problems, Outotec proposed high gradient magnetic separation to remove chalcopyrite from the galena. Doubt if it would be applicable to galena/sphalerite separation unless the sphalerite was actually marmatite.

Interesting observations about galena recovery in columns! The Cadjebut lead-zinc operation had a problem where a large surge of galena concentrate would erupt ('burp' as the operators called it) from the column and disrupt the cleaning circuit performance for hours, only to repeat again and again.

Analysis showed that it was due to competition between the various galena particles - that is coarse versus finer - to report to the top of the froth bed and exit from the column as concentrate. This situation is exacerbated in a column where there is a very deep froth, and in the case of Cadjebut, a very coarse grind size. I am sure this phenomenon happens to some extent in all lead cleaning circuits where there is a coarser size fraction present.

So the coarser particles were 'held' at the bottom of the froth bed until a critical 'amount' was achieved and they forced their way to the surface of the froth bed - or so it would appear.

I like them in roughing applications and in cleaning applications; they definitely need at least two stages of conventional banks following them (circulating loads, changes in mass pulls, etc.) [Viz. hybrid circuit]. Anyway, if anyone is interested, I wrote quite a few papers on these topics in the late 80s and early 90s.

Agreed to your strategy that "stopping things from happening" or in other words prevention is better than cure. The root cause may be the one or combination of many like influencing ions coming from mine or the part of same may recycling along with the recycled water from dewatering section of flotation plant (may be inefficient dewatering or the recycled water needs a nullifying treatment effect). This is also differing mine to mine and place to place. So when we presuming/ experiencing one or more root cause then solutions may also be in multiple.

Similarly agreed to your saying that we need to live with slime and entrainment in flotation! We can reduce them to some extent with improving classification by reducing recycling of fines to grinding mills, using pulp lifters in mills, subjecting grinding at low SG, or shifting grinding to verti-mills for playing with slurry discharge height. Post to reduction is finding the effective method to nullify its wrong impact reducing the process stability or economy.

I feel it's good that we are interacting with our experience and compiling fine prints of process practices around the world and successful solution implementation.

Kindly send few such papers on column flotation. I too am fond of column flotation. I spent 4 years on industrial column to develop an innovative design for a column for Zn cleaning circuit to reduce Silica from 6% to 3% so as to make acceptable to SMELTER. 80000 MT OF Zn concentrate was rejected by smelter for having high silica. For the last 10 years column is in operation producing 3% Silica.

I will need to find these papers and 'digitise' them. Another comment that was about columns that deserves further illumination is column height: it does not need to be 10 to 12m high. Residence time is not really an applicable concept in column flotation - more volume through height does not increase recoveries since recoveries are governed by the froth phase. There was a nice paper in Column '91 demonstrating that 'short' columns were effective as 'tall' columns.

An attractive feature of roughing with columns is that you can recover final grade concentrate (as one can of the first few cells of a conventional now rarely used flotation bank) - sometimes at reasonably high recoveries (~60% : all depends on the mineralogy of course) - and bypass cleaning. With a coarse flotation stage in the grinding circuit (if mineralogy allows, well on the way to establishing a high performance flotation flowsheet.

I haven’t written any papers on columns but have probably done as much work with them as anyone on the planet, culminating in design, construct, operate of what I believe is still the only "ALL COLUMN" (no other cells) differential copper-lead-zinc circuit ever constructed back in 1991. Full benefit is best achieved by installing in roughing/scavenging duty. The "Burping" phenomenon is typical of an over-aerated column which can happen in cleaning a lot easier than in roughing due to high concentration of froth mineral and reagents. Columns are very well mixed vessels, air entrainment is facilitated by the vertical mixing action, and once it reaches 15-20% the whole dynamics of superficial counter current air\liquid flow breaks down, resulting in a boiling bath tub. The only recovery (and preventative) action is to control air addition to maintain air holdup below the critical level (easily achieved with pressure measurement in the right places).

Good concepts presented on the use of column flotation as applied to the selective flotation of galena.

However I would like to expand on above statement on "columns are very well mixed vessels". It is important to distinguish between the two types of mixing that can occur in columns: radial and axial mixing. Radial mixing is desirable, but not back mixing (or axial mixing). Operators / technical personnel should take actions to reduce axial mixing in columns. There is a fine balance between superficial air flow rate (up flow) and superficial slurry flow rate (down flow) in a column. At some point the flow regime inside a column becomes turbulent and this is detrimental to recovery. I also would like to say, one (significant) reason for burping in the froth zone in a column is lack of mineralization on bubbles (which could also be related to lack of recoverable particles, and / or chemistry of the pulp). We know, from practical experience, that some column operators, who were faced with this problem, solved their problem (only partly) by installing froth crowders in the middle of the froth zone (similar to the ones used in conventional flotation cells). As we also know the main way the air can leave a column is from the top (i.e. froth zone), where the bubbles reach their largest size, due mainly to the drop in static pressure. Some bubbles can leave from the tails end (especially if the slurry superficial velocity is much larger than the air superficial velocity. Froth layer can also see collapsing froth, if the bubbles are heavily mineralised and the heavily laden bubbles cannot be transported to nearest lip and collapse. This is an indication that carrying capacity of that column has been exceeded. In these cases, particles which are dropped back into the collection zone, will be picked up again by rising bubbles, leading to heavy re-circulation of particles between the top of the collection zone and the froth zone (by drop back and re-collection).

There are plenty of papers (theoretical and practical) in the literature to explain these concepts. Column flotation was very common about 10-15 years ago, but now their applications seem to be limited.

Wow a lot of discussion over past few days’ apologies if some of my comments/replies are getting off the original topic.

CL = circulating load, my bad I lapsed into short-hand. Usually it is a factor of column operation due to the unit’s stage recovery and/or coarser particle build-up. Generally this is managed with mechanical scavengers and a regrinds mill.

I’ve never heard of Calcmin (is it in Iran?) however froth washing is an idea that have been around for years on both mechanical cells and more commonly columns. The oldest reference I’ve seen to it is in Taggart (1927). My main experience with columns was at Lisheen.

The Cadjebut case sounds interesting I hadn’t heard of that one.

I suspect that I was once a float operator at the all column plant you’ve described, as I only know plant like this I know of is Peak Gold. My time there was 7-8 year post design. The copper columns did a good job however the lead/zinc mixed columns weren’t so good. Saying this I suspect this largely due to the lower feed grade that design and the fact there was a leachcircuit immediately prior to the column feed so some depression of the sphalerite (often in binaries with the galena) was occurring. 

Problems in columns and solutions:

Froth crowding in flotation:

This happens if collector dosage is more and bubbles accumulate without getting discharged. Discharge rate of froth again depends on froth addition. Many operators try different dosage from the original design and land in problems. Or strength of collector is high at the same flow rate then gm/ton increases and causes froth crowding. When froth becomes heavy it loses its floatability and returns back in to slurry causing boiling.

In column froth crowding:

Yes it happens when flow rate of froth to come out becomes sluggish. This may be due to less froth dosage, wt% solids is high in column. Columns in general are operated in dilute slurries less than 30 in cleaning stages. All columns are operated with froth size between 1mm to 2mm. A bed height of 500mm is idle. Froth washing is a must to reduce silica and also avoid forth crowding.

Operation of column in auto mode:

Manual mode operations are out dated and difficult to operate. All operating parameters need to be optimised and fixed, to put them to operate in auto mode, with very little variations.

PARTICLE SIZE:

This plays a major role in all quality control of both grade and recovery. Froth Crowding may be due to this also. As coarse particles on the bubbles may become heavy for a froth to carry and flow out, causing boiling, and froth crowding. Need to be optimised by adding more water in cyclone feed (Pump sump).

FLOTATION: It is both art and science. It can be operated in different ways, depends on one's experience. When compared to past 20 years to day many have developed instruments to measure all most all parameters and also control on line. Today much software is available to optimise parameters. Today operators are fortunate enough to sit in AC and control room to control the process. Different models and designs are available. For a good design of froth washing you need to have a sound knowledge of washing froth each bubble coming out.

My goodness - we have wandered away from the original discussion usefully I trust. The 'burping' I described at Cadjebut was due to this interesting competition in the froth - and certainly 'over aeration' can also be a cause as noted. I am sure that a paper was presented on your operation prior to commissioning and operation.

When discussing an ore processing issue either on grinding or flotation one usually find that everyone has looked into a problem from a different angle. As soon we start talking to other people we ALL realize that we were missing interactions. This is normal and is the beauty of group discussion. One way to find more questions in our own heart and brain is asking us why? Once we have the answer we can ask why? Again to a component in the same answer you just found but nothing imitates the richness reached in a group discussion. I know everyone knows this; the thing is that we forget to do it. We may not have time to look for all the parameters at play in a flotation problem, but guaranteed your problems start with the ore buried in that mountain; it embraces your operating practices, your people training, your water quality, your ore blends, your measurement systems and the grinding andflotation machines (I may be missing something).

As you stated, the cyanide addition didn't influence on depressing Sphalerite in both laboratory and industrial work. Also the other similar compounds like ZnSo4 didn't change the result although the amount of addition was high in industrial work (5000 gr/ton). The Sulphur compounds (like H2S) have a positive effect when it added prior to flotation cells (conditioner) but we didn't test it in milling stage because the line of production is still shutdown for technical reasons. One question still remains after your recommendations that how would be the availability and the price of trithiocarbonate compounds?

I really apologize for my late response to your comment. I didn't see your question till now when I was reading useful comments from our colleagues in this group. Yes, "Calcimin" is the big producer of lead and zinc concentrate in Iran and they use this method (froth washing on column cell) right now.

I just realized that you don't know what is causing your problem. I would say that solutions provided here may or may not help you. It is nice to hear about these alternatives though because it opens avenues to develop new solutions

I suggest that you develop a flotation DOE to determine what is the effect of each one of your flotation parameters and the effect of the interactions between them. Please don't leave the water quality out of the design. You should study the effect of pH, collector, other reagents you may use, slurry % solids, particle size. I suggest that you block your experiment in ore type to see if the ore type has an effect over your problem.

You need to determine what is driving your metallurgical performance before looking for solutions. In any case you may want to try different solutions but you may never know what actually produced a change in your system. Make sure that your lab procedure resembles what happens at plant level and that the lab test is reproducible.

Actually our main problem is the last sentence of your comment:

" your lab procedure resembles what happens at plant level and that the lab test is reproducible." We don't aware what is the best method to simulate the system and find the problem? What I am believe in this case is that "Experiments" play the main role to solve such these problems. Still we couldn't solve this problem and in our best result of galena concentrate, we have 14% Zinc in Lead product (Cannot be neglected).

Looking for a problem in a complex system is like finding a needle in a straw storage. Just Consider a corrosion of cells or pipework happens when you do not aware of that so by measuring Eh parameter how can you define what is the origin of this problem and where is it?

All my suggestion can be implemented in a lab and in a plant. All the parameters indicated above can be measured quite easily. And these procedures can lead you to a solution.

Interesting challenge! I can only offer questions and likely solutions arising from a positive answer. Is the sphalerite suffering from chalcopyrite disease? If so, you need to examine the dosage and selection of the collector used for the Pb float.

You are mentioning a high silver content in the ore. Has the sphalerite been probed for silver content in solid solution? It is possible that the sphalerite reporting to the Pb concentrate has a higher silver content than that reporting to the Zn concentrate. This would be a tough one to solve.

You are also mentioning a varying iron content of the sphalerite. Again, micro probing the sphalerite reporting to the Pb concentrate as well as that reporting to the Zn concentrate would indicate if this is the root cause or not. I have dealt with low iron sphalerite (white in the froth) and it does come extremely early in the float even in the presence of depressants.

Pb-Zn-+/-Py ores hosted in dolomitic host rocks are more susceptible to poor Pb/Zn selectivity than those hosted in siliceous host rocks. Finally, what is the pH of the Pb rougher? Too high and you may get iron-hydroxyl species preferentially precipitating on the surface of sphalerite and acting as sites for collector adsorptions.

PH adoption is done with various types of regulators such as lime and Soda Ash. Lime was added prior to milling stage (not in the circulating pump) and the amount of PH increases around 8.5 or higher. Is this PH range may lead to a problem? I must say that before we do this PH regulation with these reagents, we work with natural PH of recycling water that was in range of 7-8.

Yes, the iron content of zinc sulphide is low and it easily float with Galena although we consume much ZnSO4 and NaCN. But in the second stage of flotation (Zinc Sulphide) with best adoption of CuSO4 and Lime consumption we have bright bubbles (light yellow) in rougher stage. What do you suggest to solve this problem?

The XRD analysis Shows that chalcopyrite amount of ore is low or absent in some cases (lower than 5%) in your view this amount could be lead to problem?

As you stated the host rock of this ore is dolomitic and we gain poor selectivity for galena.

With present or absent of PH regulators in the beginning of the flotation, Nothing changed and the formed bubbles on the cell surface is like null bubbles and amount of bubble load is not the amount that we expected. (Galena % in ore is about 3%)

So this procedure is resulted in 1.8% PbS in tailing. (Recovery got lower than 50 percent). It’s good to say about classification of cyclone overflow:

+100 mesh is about 6-8%

+200 mesh is about 15-20 %

+325 mesh is the same as +200 or lower

and -325 mesh is higher than 50 %

The density of cyclone overflow is about 1450.

It will be better to have mineralogical population of ore, elemental percentage with respect to particle size, to ascertain the root cause for pre activated zinc sphalerite flotation in galena concentrate and reason for 50 % recovery of galena. It seems we have a similar ore in India galena, zinc sphalerite, pyrite, pyrrhotite, silica in host dolomite along with traces graphitic and mica.

In our case I felt low recovery of Galena is the small Galena particle size i.e. 50% passing 325 mesh, test work indicates twin flotation cell usage at optimised rpm to suite particle size will be improve but onward zinc sphalerite flotation was having bad crunch of it because of finer regrind.

Regarding pre activated zinc sphalerite floating in galena circuit the following may be looked into.

Traces elements may be activating zinc sphalerite. Zinc sulphate solution may be inadequate. Try playing in ZnSo4, NaCN, GPT in ballmill because you said it's free liberated zinc sphalerite. If the Collector selectivity is a problem then use some moderate collectors like Potassium ethyl Xanthate or increase the points of adding (May not be effective largely).

pH range of 7 to 8.5 should not give you problems here. The amount of chalcopyrite in the ore does not tell how much would be as inclusions in sphalerite. Simple optical microscopy and/or microprobe should be performed. There may be some information on that in the original metallurgical studies for the development of the flow sheet you are now using.

The few papers about dolomitic vs. siliceous host rocks for Pb-Zn selectivity dates from the 1960-1970 era - I can't remember exactly but look for the IMPC (international Mineral Processing Congress) proceedings and the CMP (Canadian Mineral Processors) proceedings from that era. I remember the observations presentation but unfortunately not if solutions were proposed.

A low iron sphaleritesuch as what seems to report to your Pb concentrate is extremely difficult to depress with the conventional NaCN:ZnSO4 combination. There is no iron in the lattice for the NaCN to attack and subsequent replacement with zinc hydroxide/sulphate. In this case, it might be worth considering a reverse flotation step as an additional last Pb cleaning step - depressing the galena.

CASE STUDIES DON IN HZL VEDANTA for burning problems of ISM, Zn in lead etc.

ISM, GrC: In RDM mine this problem was a very serious concern, 80000 mt Zinc concentrate was rejected by smelter for high ISM. After adding COLUMN flotation and innovative froth washing system ISM came down from 8 to 3.

Similarly Gr.C and Zn in lead. Circuit: It was observed that coarse grains reported in cyclone over flow. Could not be controlled after changing wt% solids to cyclone. Vortex finder and apex sizes also tried. It was observed that residence time was less in cyclone. Long cone also called as G-Max supplied by Krebs were found to solve the problems.

Bulk Flotation Pb -Zn: Many a times it was attempted to feed Pyro metallurgy smelter with bulk concentrate. It was used for several months but no reason given for stopping. May be due to ISM problem. COLUMN was not tried for this bulk concentrate. May be it is the right solution today.

Bulk Flotationof Pb-Cu: Yes there was a problem of use of Dichromate for separating Pb-Cu. This problem of pollution was avoided by floating bulk Pb-Cu.

Heavy pyrite in Zinc. Con.: It was observed that spillage pump below regrind ball mill ----Pump discharge by mistake was given in Zinc cleaner cells.

Zn In Pb: Heavy spillage form Zinc circuit was fed to lead circuit, by mistake. Excess dosage of NaCn was used to depress sphalerite in LEAD circuit.

YOUR PROBLEM:

I saw particle size distribution given by you. Your problem is similar to HZL RDM. Change your cyclone with G-MAX KREBS to avoid coarse reporting in over flow. Hope you problem will be solved. Did you do technical auditing with the plant Design parameters used for designing. Compare all parameters and find solutions. 

The Idea of reverse flotation was done with reagents like potassium dichromate and sodium dichromate. But when we did such a test in laboratory, by low dichromate consumption, weight of concentrate decreases and when we increased dichromate consumption, the surface of lab cell covered with null bubbles (nothing floated), I think this reagent will depress both sphalerite and galena. May you suggest me the reagent that depresses only galena not sphalerite?

Also we used quebracho (polymer) to depress zinc sphalerite in both reverse flotation of concentrate and in the beginning of Galena flotation in rougher stage. Quebrachos have the same effects like dichromate as we saw in laboratory.

Potassium permanganate also applied to depress sphalerite in lab test but the result was not successful. I must mention one of our colleagues, comment in our last discussion, He stated "Flash flotation" of sphalrite:

" I call it partial activation. Add a little copper sulphate (and I mean a little, like 10-30 grams per tonne and assuming that activation isn't already occurring) to pre-activate some of the sphalerite. Then run a flash float to pull off a sphalerite concentrate using a copper selective collector (dithiophospshate/thionocarbamate blend). You'll find that activated zinc will float a lot faster than the galena. The resultant tails will then, hopefully, look like a regular type lead/zinc ore (-2% galena, -7% sphalerite or so). "

This procedure was done in a lab test but again what we saw was activated zinc float prior to galena. Again the result of this test was the same. You are right, as you stated we add our depressant either to milling and before milling, also we add sodium phosphate to prevent zinc activation by lead dissolution. It didn't answer perfectly as we expected.

Thank you for your suggestion, to apply such these changes (hardware change) it takes much time to buy, Supply and installation of this cyclone but I will follow your suggestion.

Summarizing the observations:

Sphalerite with variable iron content in solid solution; the low iron one is the one floating easily in the lead circuit. High silver ore - unknown silver content in solid solution in sphalerite (should be verified as a high content would lead to sphalerite behaving as it was "pre-activated"). Likely not a chalcopyrite disease issue. Not a locking issue. Not a process water quality issue.

The idea of floating the zinc first suggested has some merits.

To minimize changes in the plant, one could consider a flash/partial zinc float with a thionocarbamate collector (which does not collect galena). Just float what easily comes and direct this to the zinc cleaning circuit. The rest of the lead rougher (and the plant) would essentially remain the same.

The trick will be to figure out where exactly to "cut" the rougher launders to direct the appropriate concentrate to the rest of the plant - from laboratory flotation tests.

Long time ago after the last discussion about this pre-activated zinc sphalerite problem in a Pb/Cu circuit. Assuming you doesn’t have liberation problems, and then the most important issue is to quantify how much of the sphalerite is being floated in the Pb concentrate and its relationship in the size fractions. As you mention before, most of the particles are in the -325 mesh; so, the contribution of the sphalerite in the Pb concentrate may be a combination of true flotation (pre-activation) and entrainment. An issue that you should consider is the association of Ag/Pb particles, a high dosage of ZnSO4 (used to depress sphalerite) in the Pb/Cu flotation will depress Pb particles, especially if the pH is increased. So far, I'm guessing that you have got high Zn grade (17 - 24 %Zn) in the Pb concentrate but the zinc recovery must be less than 10-20% in the Pb concentrate. Therefore, I strongly recommend carrying on water analysis to determine (quantify) what type of ion metals is in the solution to know what metals are activating the sphalerite at the front of the process (milling - normally due to ions of Ag, Pb, Cu and Fe). If the pre-activation of sphalerite is due to Ag/Pb ions then I recommend using sodium sulfite, bisulfite or metabisulfite; if you have ions of Cu, ZnSO4, NaCN or the mixture(ZnSO4/NaCN) must be used. Be careful not to over dosage with these depressant because you will be depressing Pb/Cu particles as well. The most important issue to solve this problem is what reagent can use to form stable complexes with soluble ions metals.

Far back in the comments, I mentioned Pb ion activation, do not underestimate it. Likewise Ag ions. I agree that low Fe sphalerite will always activate first, this is indirect proof that the issue is chemical activation. If you have not done it yet, do proper TOF-LIMs on sphalerite particles in your lead conc. identify the predominant surface activation metal, and apply the appropriate chemical (complexing) solution.

I would like to say that not only this problem couldn't solve, it appears in another company running the same kind ore of mixed sulfide-oxide Pb/Zn. After all of my experiences I come to this conclusion that this problem would arises in any flotation of this kind.

You mentioned "simple EDTA extraction test”, I’ll be glad if you describe this method that if we have access to such this test we’ll do it. We do the "flash flotation" in our industry but sadly we didn't success. Galena came to ZnS conc. So we change our flow sheet to what we did in processing of this ore that Galena would be first to float. NaCN and Zinc Sulfate didn't work for depressing pre-activated zinc sphalerite, so we add sodium sulphite in milling stage and this one didn't work either.