The behaviour of lead/zinc ores in industrial flotation circuits with reference to simulation and control

The flotation behaviour of minerals in lead/zinc sulphidenores was investigated for the purpose of developing mathematicalnmodels suitable for incorporation in an automatic control system.nEmphasis was placed on the collection of steady-state data from industrialncircuits. Plant tests were conducted in two concentrators treating ancoarsely mineralized lead/zinc sulphide ore and in one concentratorntreating a complex, finely disseminated copper/lead/zinc/iron sulphide nore. The effects of changes in rougher retention time, collector andndepressant additions, and important physical variables wereninvestigated to determine the suitability of the variables for usenin control systems. Laboratory test work was used to confirm andnextend observations made in the plants.nWater was treated as a fundamental component of the flotationnprocess. Its rate of recovery affected the rates of recovery of allnminerals in the feed. The more water-avid the surface of a mineral,nthe greater the importance of the water entrainment mechanism in itsnrecovery. Therefore, the effect of the rate of recovery of waternincreased through sulphide valuable, sulphide gangue to non sulphide ngangue. To develop a control scheme for a galena rougher scavengerncircuit, the importance of the water must be recognized. Pulp level,nair addition, and collector and depressant additions are the mostuseful short-term control variables but variation of roughernretention time is also useful for minimizing zinc sulphide recoverynif ample capacity is available. These conclusions were based on thenobservations thatn(a) although the total recovery of valuables was insensitivento the rate of collector addition on the flat portionnof the plateau-type response curve, initial flotationnrate was affected. The control philosophy with nrespect to collector should be to use the initialnflotation rate as a sensor to permit minimizationnof the consumption of collector rather than to use its addition rate to vary valuable sulphide/ganguensulphide selectivity. nn(b) alteration of froth depth by variation of pulpnlevel changed valuable/gangue selectivities and couldnbe used to minimize both sulphide and non sulphidengangue recoveries at an acceptable recovery of valuables,nandn(c) prolonged retention times in lead rougher banksnincreased zinc sulphide recovery in the leadnconcentrate without significantly increasingngalena recovery.nImpulse tracer tests were used to examine the mixing regimesnin industrial flotation banks. A model was developed to predictnthe movement of soluble tracer through a series of perfectlynmixed compartments. Allowance was made for tracer and volume losses nin the cell concentrates. The model can be used to detectndeviation from ideal mixing conditions. nThe material transfer processes operating in the froth volumenwere investigated in steady-state continuous pilot scale tests. A nmodel was developed which permits prediction of the recovery ofnvalucible and gangue minerals by direct entrainment in the water nwhich reaches the concentrate. The recovery rate of water not onlynaffects the drainage of entrained mineral from the froth but also nthe drainage of hydrophobic mineral which reaches the base of thenfroth by attachment to air bubbles. A drainage model was developednwhich described the effect of varying water recovery rate on the nrecovery of valuable and gangue minerals in a series of plant tests. n