Roast Reaction Processes

Today roast reaction process (Direct reduction process) is very popular to produce lead .This process has the following advantages such as:

• The charge material is powder, therefore it doesn't need high maintenance cost for sintering machinery
• It doesn't need expensive coke fuel for reduction
• This process needs high grade ore, which will be produced by Flotation process
• The most energy from the exothermic reaction will be used

Chemistry reaction and Reduction Mechanism

Lead sulphide reacts with lead oxide or lead sulphate to form metallic lead and sulphur dioxide in the roast reaction:

PbS +2O₂=PbSO₄ , ∆H₉₀₀=-191/9 Kcal

2PbS+3O₂=2PbO+2SO₂ , ∆H₉₀₀=-188/4 Kcal

PbS +PbSo₄=2Pb+2SO₂ , ∆H₉₀₀=+94/4 Kcal

PbS +2PbO=3Pb+SO₂ , ∆H₉₀₀=+40/9 Kcal

The last reaction is very important in the metallurgy of lead, therefore the studies of the thermodynamic variables are based on this reaction:

K = a³_PbxP_SO2/a_PbSxa²_PbO = e^-∆Go/RT

Base on this equation; for decreasing the a_PbS ,it is the following possibility:

• decreasing PSO₂;it means that SO₂must be removed from the furnace
• increasing PbO; the oxidation must be so managed that lead oxidized and goes to the slag
• Increasing temperature, which it is not suitable in the technical process

Regarding the above comments the roast reduction process must be occur in two steps; Oxidation and Reduction steps. The oxidation process will be occurred regarding the above reactions. After this process the lead in the slag must be removed through a reduction process.

For the reduction process cokes are used .The reduction of PbO with cokes an CO are as follow:

C+1/2O₂=CO

C+O₂=CO₂

PbO+ C= Pb+ CO

PbO+ CO=Pb+CO₂

2PbO+PbS =3Pb+SO₂

The last three reactions are endothermic therefor in the furnace and the roast reaction process electrical energy or Ignition will be used

Technology in Roast Reaction Process