Flotation Tank

The froth flotation process has been employed to concentrate valuable minerals since the last years of the nineteen century when the process was introduced in Canada, and has been practiced in the machine called flotation tank or flotation cell whose design varies with the manufacturer. Nowadays, the main change in the froth flotation practice has been to use large cell which are bigger flotation tanks. The large flotation cells are the obvious choice for a new concentrator and at existing plants; they offer an economic way of increasing capacity and reducing operation costs. The performance is related to product recovery and concentrate grade, capacity in tons treated, power draw, maintenance costs, and operating labor cost per ton treated.

Essentially a flotation machine employs a standpipe, hooded impeller closely baffled by a stator, and the inlet ports in the hood for slurry circulation. One type can be self aerating and other designs use hollow shafts for aeration in place of the standpipe, and air is injected under slight pressure. Other designs can have inlet ports below the impeller. It necessary to indicate that all the designs exist competitively and all have their adherents and critics. To understand and realize the coexistence of this wide range of design it is helpful to be focused on similarities in the parameter values that describe their hydrodynamic behaviour and consequently its metallurgical performance.

Simply one person can say that a flotation tank must to form and remove a mineralized froth, but the functions really are an aspect very serious at the moment of designing any flotation cell. Thus, the functions can be grouped in three categories: material handling, floatability effects, and separation effects.

The materials handling involves feed entry, tailings discharge and froth support and removal. Initially the designs considered introduction of the feed directly to the impeller zone, from below or from the sides of the cells. Now, it is common to find a feed box at the head of the cells with the slurry passing cell to cell, either over or under between cell partitions. End tailings discharge over adjustable weirs is standard, as are adjustable relief ports. The cell contour can be rectangular or circular, only depends of the manufacturer’s criterium. Mechanical froth removal was used initially but actually, most design offer a froth removal by overflow.

The floatability effects involve dissolution of water soluble reactants, dispersion of water insoluble reactants, attritional effects on particle surfaces, and promotion of mineral surface-reagents (i.e. collectors, depressants, frother, and air). The fact that sulphides were the first to which flotation was applied masked the important aspect of the conditioning. The pulp in a cell is subjected to intense agitation. It no only does the separation process itself go on, but so do many chemical and surface-chemical processes involving diffusion of reagent to mineral surfaces, interaction between surfaces and dispersed insoluble liquids and abrasion of surfaces as a result of the physical contact with other particles or will cell parts.

The separation effects are related to particle suspensions, air entrainment, air dispersion, and provision of appropriate conditions for particle-bubble interaction. The separation process itself consists of aggregating floatable particles with gas bubbles and providing a means for a froth to form and be removed.