Zinc Concentrate Roasting Process in a Fluidized Bed Furnace

Zinc Concentrate Roasting Process: 850 T/day Capacity

Blende-Roasting Furnace and Heat Recovery Steam Generator

This includes the furnace that carries out the oxidation of ZnS, the heat recovery steam generator for cooling the gas, and the partial removal of solids carried by the gases.

Treatment Water for Steam-Water Circuit

This is the demineralized process water. This water will be used in the heat recovery boiler and furnace beams, which form part of the same circuit.

Purification of Gases from Roasting

The functions of the gas produced are to eliminate impurities and reduce the gas temperature for treatment.

Contact and Absorption

This is the transformation of SO₂ into sulfuric acid for reuse in marketing or the leaching stage.

Feedstock and Products

This is a zinc concentrate obtained by a flotation process, which requires roasting. The concentrate mix has a specific chemical composition and granulometry. The relationship between the concentration of Cu (copper) and Pb (lead) in the mineral is important to ensure smooth furnace operation. To control the particle size of the bed, a sample is taken and passed through a 1mm sieve to determine the percentage of rejection.

Transport and Storage of Concentrates

This installation consists of a system of hoppers, conveyors, and transfer towers. For the removal of metal bodies, a magnetic separator is arranged at the end of a conveyor belt. This consists of an electromagnet and a belt carrying metal objects attached to it, leading to a hopper for collecting them.

Roaster

The reactions that occur are very complex. The most important reaction is the oxidation of zinc sulfide. Through this exothermic reaction, ZnS is oxidized. The ZnO obtained must meet strict requirements for subsequent leaching. It must not contain more than 0.3% sulfur as sulfide and 1.8% sulfur as sulfate. Therefore, the formation of zinc ferrite must be avoided as much as possible. For roasting the blende, a fluidized bed furnace is used. This is based on obtaining a mixture of sphalerite and air, blown by the furnace blower through the wind box.

Description of the Process

The air introduced by the furnace blower provides SO₂, dragging the gas produced by the roasting process elements along with some roasted ore of finer granulometry towards the heat recovery boiler. The thicker mineral grain remains in the furnace bed until it overflows. Some plates are of different sizes and are positioned to adjust the bed height and, therefore, the furnace pressure. This overflow is led by two pipes to a cooler or trommel, which reduces its temperature by a primary circuit with water, which in turn is cooled in a secondary circuit with cool seawater. Once cooled, the calcine is directed to the ball mill to achieve a grain size suitable for treatment in the leaching process. The gas, dragged along with the fines from the fluidized bed, enters the heat recovery boiler. In it, the gas expands, increasing the surface flow velocity, and the particles precipitate. This is aided by the numerous impacts of small calcine particles on the water-vapor system bundles. The precipitated calcine is collected by a chain conveyor or redler and is discharged to the trommel. The finer particles that have managed to come through the boiler enter the hot gas electrostatic precipitator, where the gas is separated by strong ionizing electric fields. A chain conveyor collects the precipitated calcine and returns it to the collection system downstream of the mill. The calcine collected at this point is very small.

Fluidized Bed Furnace

The fluidized bed furnace is a key component of the zinc concentrate roasting process.