I believe we discussed this topic in another forum about the concept of froth equilibrium height.  The idea of testing at different froth heights is a good one.  What we recommend in plants that have good control of the pulp level is to actually measure the grade at various heights and establishing a grade gradient versus height 0 froth height up to the FEH.  Just lower the pulp level in increments and take sample of the overflow and analyse them for grade.  You could also analyse them for particle size as well.  What you would expect is that the higher the froth height, the more coarse you would lose and the higher the grade.  The problem is that the pulp level is very hard to control in a float test unless you have a special cell that will do this.  But the concept is the same.  Establish a set of conditions like frother dosage and type, air rate and measure the FEH.  Then do flotation tests using various froth heights.  4 should do.  Just make sure that you use initial conditions that can give you a good high FEH.  This will allow you better control of each test.  If the conditions give you too low a FEH, you cannot get the precision you need.  Also make sure you perform the tests all the way to the just below the FEH because you will find that the biggest changes come when you are about 25% from the FEH.  Good luck.

There are a few other considerations you need to look at when you are looking at froth height vs concentrate grade and screen analysis. Frank gave you some the measurement of grade gradient which would be applicable for continuous reactor. For the lab, you can do the same test but need to refresh the feed after level sampling. In all, there are other considerations:

Getting a correct level. When we (At Aminpro) want very accurate level control in the lab, we have a unique setup consisting of a water reservoir located above the cell that receives water from a main stock tank placed on the floor. The reservoir has two outlets at the same elevation: one connected to the bottom of the flotation cell and one to overflow to a water stock tank. If we ensure that the water pumped from the main stock tank to the reservoir keeps water flowing back to the stock tank, the loops is then automated. The reservoir is attached to a manual gear level positioner such that we can set its level at a desired position. As the density of the pulp is higher than that of water, the reservoir o/f pipes will always be higher than the cell. The difference can be calculated in your spare time. Then you need to adjust for air holdup…another gem to account for (hint: check the level with air and without air and estimate air holdup).

Changes in Froth Recovery (Fr): when you change the froth bed height, you are indeed changing the froth recovery and therefore the overall cell recovery from the following, where Rflot is the flotation recovery and Rc is the lab collection zone recovery Rc = (1 – exp(-kt)). Rmax. You can determine froth recovery by doing a few froth bed heights and extrapolating to zero height.

Entrainment Recovery of solids (Re): various degrees of entrainment (D.E. = Re/Rw) come into play when you change the froth bed. For one you tend to entrain more water (higher water recovery (Rw) when the bed is shallow, and with it more solids. The changes in the degree of entrainment (D.E.) are huge and well defined for industrial processes when you change air and froth depth. It closes the calculation of total cell recovery with the following expression:

Now you have the full picture….but yes, leave items 2 and 3 out and follow Frank’s notes.

Roger Amelunxen

911Met-Pabloski.pdf

https://www.911metallurgist.com/froth_flotation/how-to-froth-depth-change/