You asked a very good question.

I like the shape of the cells G-Cell http://is.gd/ThexPu and Jamesonhttp://is.gd/qTOB3t

Yes, Jameson cell has completely different feeding arrangement and there is no mechanical agitation inside the tank. It is the pressurized slurry feed into the down comer part of cell which creates agitation. I was involved in Jameson cell pilot testing once but haven't worked with commercial scale Jameson cell operation so can't comment but it must be having its own pros and cons especially with maximum feed particle size as there is no mechanical agitation.

Good question with some interesting points raised.

The mixing (and gas dispersion) in a cylindrical cell is always going to be better as it has a more even geometry. You are also absolutely correct that as cylindrical cells can be setup up as single units each with their own air and level control they generally give better control and performance. The comments on the operating cylindrical cells and sanding/settling problems are interesting and I could point you to 1,000s of instances globally where this in not the case with even large 300m3 and 500m3 cells. In most cases the cylindrical types cells should handle coarse particles better - to this end there are a number of large copper concentrators that operate 300m3 cells with feed P80s of 200+ microns. From the description you give I think that either these tanks were not designed properly or are not being operated as designed.

Firstly, if there is sanding in the tank itself then there is likely a problem with the mixing mechanism. Either the mechanism is too small for the duty or is running too slowly. Alternatively the mechanism could be worn to the point where it is not an efficient pump hence material starts to settle – this is common on many sites where maintenance tries to save money but not replacing mechanisms in a timely fashion – if in doubt ask the manufacture to come along and have a look during a shutdown.

Secondly, the sanding in the tank (and ducting /piping between tanks) occurs typically due to lack of velocity in this area. If flows are lower than designed there may not be sufficient velocity in the un-agitated zones between the tanks and the larger particles begin to settle. This can be addressed by reviewing the design and making sure that is suitable for the current flows and particle size distributions and re-engineering the ducting and valves accordingly.

There is a third, common cause that I’ve seen of tanks / valves sanding up. This is when large tramp objects and rocks (typically from a blocked cyclone) enter the floatation cells. I’ve seen rocks and ball chips over an inch in diameter build up in flotation trains. This situation is usually worse (and can stop production) when discharge valves are elevated up the tank wall or when the cells are the type that rely on a false bottom for their pumping action. This can be prevented by mechanical protection (e.g. a screen in-front of the flotation bank, but this isn’t always an option due to capital cost (especially with large concentrators). As this situation will likely happen when operations push tonnage the best way to minimize its impact is provide a mechanism for these to tramp particles to pass through the cells. To this end using cells with down-flow type darts (ideally located in the tank itself) will allow these objects to pass through the cells to tails. Other arrangements such as sand-gates can be used (or retrofitted) if the cell has or needs an elevated valve outlet.

I wrote "I like the shape of the cells G-Cell"

My cell classification (book "Fundamentals of the theory of flotation") in Spanishhttp://is.gd/G2DK5P 

Operational re liabilities and metallurgical performance comparison of similar application flotation machines needs similar feed inputs and operation parameters in regard like ore mineralogy (population, species and their grain size distribution), residence time, froth launder lip length/ unit cell volume, pulp densities, gas feeding, reagents dosing gpt, energy consumption /metric ton of ore, conditioning time turbulence level ) and etc. The above are required for fair comparison post to the perfect design and similar degree of adaption in operation.

Some plant operators say silver recovery in Ok u bottom cells is bit better than tank cells in ore having galena, spharalite, pyrite, pyrohotite, which needs further to be confirmed.

Agreed, that in macro level comparison, tank cells are better than u bottom cells but in micro level and ideal condition it's difficult to compare and finally study may ends at cost benefit, rate of returns analyses on investment increase.

sanding these days at the plant and the major reason of this problem is imperfection of cyclones function that it follows of ball mill or SAG mill screen rupture or reject shortcut. At this case in addition of inefficiency in flotation process, mechanical problems like Pumps destruction, abrasion in pipes and cyclones, agitator abrasion or chocking and etc. will happen.

Your point is valid that comparison should be done considering similar operational parameters. And in fact my query was related to settling issues due to design differences between U bottom and cylindrical tank cell considering all the operational parameters same.

And yes, even I have heard that silver recovery is better in U bottom cells which make no sense, since it completely depends on the interlocking of silver with galena or sphalerite.

Agreed that u bottom cells will have more silting because of its geometry and design.

Regarding silver recovery comparison, should be followed post to the attaining of similar liberation level feed.