I have installed Flash flotation with ball mill cyclone underflow as feed to cell. It works wonders.

Actually I need a trick in flotation procedure (maybe a chemical reagent that play deslime role) for floatable lead particles that trap among these slimes.

Usually there trick is not to create these fine particles to begin with! Perhaps look at screening as an alternative to cycloning. Good flotation always begins with good comminution practices.

For your actual question try a sodium silicate (perhaps A60) as a dispersant. Or do the floats in a more dilute (lower % solids) pulp.

Is the Issue that the lead minerals will not float?

Or is the Issue that when the lead minerals are floated also many other minerals are recovered causing low grade product? The solution to each of these flotation issues is different. In my experience, when people say their minerals will not float, they actually mean the second issue; the minerals will float but not achieve suitable separation from the gangue minerals. Are you using a laboratory flowsheet of the rougher and the three stages of cleaning to try and achieve an acceptable concentrate grade?

What flotation density are you using in the roughing and cleaning stages?

Actually by trying the different amount of sodium silicate, the result in both of laboratory work and industry were the same. I think we must apply some kind of reagent that specifically related to disperse of Fe mineral gangue (bolutavic, Handbook of Flotation reagents, Vol2). As before I stated, I should also say that, the high amount of our lead is lower than 30 microns or lower than that!

What suggestion would be remains here to achieve the best result?

We would lose more than 40% lead if we use desliming methods and remove them before flotation procedure. Our minerals float but with low recovery, (50%) That’s not acceptable against the power consumptions and worker payments! The grade of lead product is higher than 60% and sometimes near 70%! But why we have a low recovery, that's remains in a question form! We try different both laboratory and industrial flow sheets and increase and rather decrease the cleaning stages to achieve the best efficiency but in both cases rather decrease or increase resulted the same recovery. The density of pulp in the beginning of the line is about 1200 and at the end of the line it decreases to about 1040.

Thank you for the feedback and information. Yes, 50% lead recovery is not acceptable. Is this 50% lead recovery the rougher recovery in the laboratory? How long are you floating for in the rougher stage? Is it 5 minutes?

What is the effect if you float for longer time in the rougher? E.g. 10 minutes? Does this increase the recovery and by how much?

If you lower the % Solids in the laboratory flotation rougher to a very low point, say 5% solids, and then float for a long time say 30 minutes and add a lot of collector 300-500g/t of collector, does this achieve a high lead recovery? But at a low lead grade?

I must appreciate your cooperation.

The laboratory results show the recovery is about 60%! The conditioning duration for each stage is about 2 minutes and the duration for collecting the froths from laboratory cell is 1 minutes of interest.

Although this results achieved from a laboratory cell with low duration of stages, the industrial work show the opposite of what we saw in laboratory with higher duration of stages. (We mentioned all of the parameters including s/l %, cell volumes, etc)

And answering your other question, I must say No, I didn't do such kind of this test you suggest. I will do that. But why lower density? 

The methods below can be used to help diagnose why the lead minerals have poor flotation recovery. You said that you achieve low lead recovery in the laboratory rougher flotation, to increase the lead recovery the following methods could be tested. Adding increased collector addition should increase the recovery. Adding increased air rate in flotation should increase the recovery. Floating (collecting froth) for a longer time should increase the recovery.

If the froth looks very weak (bubbles breaking easily) then you may want to add one or two more drops of frother to help make the froth stable. Also you said the slimes in flotation are stopping the lead being recovered. Operating the float at lower % solids will allow the particles to spread out, and allow the bubbles to connect to the fine lead particles better and the gangue slimes should be moved away from the lead particles and therefore not hinder the bubble attachment to the lead particles.

Lower % solids will also lower the viscosity in the pulp which will help improve bubble attachment to the valuable minerals. Lower % solids will also reduce the gangue that is collected to the froth by entrainment, producing a higher grade concentrate. You may also want to look at what grinding media you are using the grinding stage.

If you are using mild steel balls, then you may want to change to stainless steel balls or ceramic balls, to stop the Fe++ ions from the mild steel media from forming FeOH precipitates on the surface of the fine lead particles. These effects that are normally seen in grinding circuits with steel media, and have been discussed in the paper below, and the FeOH effect shown in Figure 4 and the Eh effect is shown in Figure 1 in this paper below.

The critical importance of the grinding environment on fine particle recovery in flotation.
Minerals Engineering, Volume 22, Issue 4, March 2009, Pages 386-394 Stephen Grano

Link Below:
http://is.gd/UH2uRk

Some customers have the same problem with low recovery of very fines particles most of the problems we have found are the following

Degree of liberation, do you have determined if your fine particles are liberated? usually fines particles are locked particles and using conventional grinding and flotation you are not going to increase recovery

If you have very fine liberated particles is necessary to avoid over grinding of this particles. So first at all you have to quantify your by-pass in classification if you have >20% by pass you have to improve your classification performance. Diluting overflow as much as possible. If you don't have higher fines by-pass, you can use a flash flotation it’s very useful to float coarse and fine liberated lead.

Floc-Flotation, if you have higher slimes and clays, you have to use a combination of dispersant + cell speed + collector +non polar reagent, when you are using dispersant you have to increase cell speed to avoid slimes coagulation and collector to improved liberated particles flotation. There is a technique, known as floc-flocculation to improve fines particles flotation.

Also we have some applications were fines and coarse particles are splitted to improved flotation time, this is due lead coarse particles gets higher kinetics than fine particles. So if you don't have enough flotation time you have problems try on lab!

I totally agree with your idea about particle interlocking, and the grinding stage is the basic issue of this problem. The recommendation of dispersant (like sodium silicate) and cell speed didn't work. But I think the other recommendation of Floc flotation will be work very well but to be honest I didn't test it. Diluting the pulp is very helpful as the results show this issue.

I would be glad if you have any experience in Floc flotation of lead slimes, share with us! Or refer me to some industrial reports about this.

I don't know what chemicals you are using. But my rich experience in Pb-Zn flotation we have used following

LEAD CIRCUIT
Sodium cyanide-to depress pyrite.
Zinc sulphate -to depress Sphalerite.
PottasiumIsopropyle xanthate-To float Galena.
MIBC—frother

ZINC CIRCUIT
Lime to maintain pH.
Copper sulphate to activate Sphalerite.
SodiumIso-propyle xanthate--to float Sphalerite.
MIBC --as frother.

You have not sent any data on technical auditing. How we can tell solution. What is Technical auditing?

Optimisation of grind size and wt% solids ---for grade and recovery for Galena 1st, then for Sphalerite.
Permutation and combinations of all reagents and their optimisation for Grade and recovery.
Very-very-important-Specifications for all reagents, and their conformity to specifications 100%. Any deviation in this will result in poor metallurgy.
Optimisation of bubble size, tank cell design, forth removal, and many more. Each stage you need to pass one by one and confirm operating parameters. In mineral processing the toughest process is flotation. You need to be more practical than theoretical.Can you educate us about your plant?

Capacity.
Quality of balls used,
Type of liners used,
Pulpdensity

All the comments are relevant and like you mentioned reagent suite is probably the most critical influence on such a circuit. Solutions like a unit cell on the mill discharge etc. will probably be a more strategic, long term and high CAPEX kind of solution. I am not sure of your reagent suite but my experience is that lead tends to oxidize on surface in the liberation process in the mill. To address that it is critical to dose both your collector and depressant SNPX and NACN in our case in your milling process. The NACN will clean the oxides and promote the collecting process on the sulphide surface and depress the Fe and Zn bearing minerals. If your process is not running accordingly this will be something cheap and quick to try.

I appreciate your complete recommendations.

The plant works 20 t/h and the balls used in the ball mill is old steel ones. The pulp density at the beginning of the lead flotation line is about 1200 and we decrease it to about 1120 and lower to achieve better recovery. I agree with you to some extent, maybe the process of oxidization in milling operations is one of the other things that bring down the recovery of lead flotation. The NACN is a good choice but by taking into consideration that the tailing of this processing will be prepared for zinc smelting unit, it will be so dangerous to make toxic steams for workers and personnel. Would be another choice that we can replace that with NACN in this kind of process?

Have you tried increasing impeller speed during the latter period of your bench floats?

If you see an increase in recovery of Pb, this will at least tell you that the fine galena is hydrophobic enough. You just need increased energy input to increase particle-bubble collision frequency and energy. A similar effect can be achieved by doing the same later down the bank on plant or reducing solids % as suggests. Though the latter will affect throughput!

Just for the record, for most conventional processing flowsheets, the final lead concentrate typically has a size less than 30 microns and typically less than 20 microns. This arises due to a combination of the brittleness of galena and the effect of the hydrocyclone: for example, if the grind size is P80 of 74 microns, then the P80 of the galena in the overflow will be 26.5 microns. So the fineness of your galena is not unusual.

You say that your issue is galena recovery and that there is also high entrainment - presumably in the zinc concentrate. IS this correct? If that is the case, then you do have a recovery problem, since the galena of all sizes is readily floated prior to floating the zinc - which typically requires coaxing i.e. activation.

There is also a mystery iron sulphide (?) mineral it is possibly marcasite or framboidal pyrite or indeed pyrrhotite? You don't mention any issues with mineralogy (i.e. all the lead is present as galena) or with pre-activation (i.e. floating of the sphalerite in the lead roughers - no lead 'oxides' present in the feed).

Two things come to mind: one is that you have an exceptionally fine galena particle size range, below 5 microns, and either surface oxidation or bubble contact/attachment are issues. However, very fine galena is recovered in several operations.

Due to surface area effects, fine galena would:

Require collector for flotation; check that sufficient collector is present
Would consume more dissolved oxygen (see following paragraph)

The second point is that galena requires dissolved oxygen to be present for maximum recovery - the presence of oxygen consumers such as the iron sulphide minerals mentioned above coupled with a fine grind in steel liners/lifters and mild steel media will strip the dissolved oxygen out and the dissolved oxygen level is not fully replaced with the cell aeration during the available flotation residence time.

A classic example of this was at the Elura (now Endeavour) Pb-Zn-Ag operation in northern NSW Australia. The pyrrhotite bearing ore required a very fine grind with mild steel media and had an oxygen conditioning stage prior to the lead roughers. Up to 10% extra lead recovery was obtained with this approach, sometimes more depending upon the slurry chemistry (ActifloatTM, BOC Gases).

Anyway, you appear to have an interesting problem and a little more clarity is required in a couple of areas for your on-line colleagues to be of more assistance.

Using cyanide in flotation process is the same as using cyanide in gold heap leaching process - cyanidation (agent NACN) must be performed in basic environment! (pH=8-10-11) to prevent generation of HCN (very toxic gas) because of possible presence of acids as H2SO4, H2CO3 ( CO2 from air), To prevent this process it is added lime as admixture. Alkaline chlorination is the technology for cyanide compounds destruction (process destroys most cyanide except iron cyanide and more stable metal-cyanide complexes). If some HCN volatilize to the atmosphere it is destructed by natural oxidation process. NACN concentrations are very low-in barren solution it is about 200 ppm (0.02%). For using cyanide must exist National Standard also in your country.

Just a quick one, try floating your plant tails and concentrate and any other streams you wish in the laboratory, then report what is happening. Is the flotation continuing i.e. recovery still improving in the lab cell, with the concentrate is the grade improving or is it all just floating and entrainment is keeping grade low? Work with your plant streams in the lab, see what is happening there, they will give you a great indication of flotation performance, plus you get the plant pulp electrochemistry and now you can play with the reagents too. He gives a good breakdown on what is required for flotation control; use those with plant float streams in the lab cell. 

Technically -45 microns is smiles so in your gauge so discover those elements. Is it valuable elements for recoveries or for what do you determined those.