Efficient Bauxite Grinding System for Alumina Refinery

Hi Friends,

Size reduction of mined ROM bauxite is essential for improving its reaction with caustic soda for dissolution of alumina (Al₂O₃) forming sodium aluminate (NaAlO₂). Coarser bauxite particles affect the alumina extraction efficiency however fine bauxite creates acute problems in settling of residue in decanters and washers. Thus optimum particle size is the basic requirement for efficient Alumina refinery. Generally, particle size in ground product slurry of bauxite is minus 10 mesh  with over 80% of minus 65 mesh fraction is considered as optimum operating parameter.

Selection and sizing of bauxite grinding equipment is carried out on the basis of following major input parameters-

• Bond index of bauxite,
• Grinding rate,
• Feed size (F₈₀),
• Product size (P₈₀)

In most of the existing Alumina refineries, ball mills are operative. Few plants in the World have rod mills and a few have two stage grinding system with combination of rod mill in first stage and  ball mill in the second stage. It has been practically seen that ball mill generates more fines compared to rod mills.The cross section of a typical Ball mill has been shown below just to have the physical feel of the main components of Ball mill and movement of grinding media inside the mill in running condition. I acknowledge with thanks the efforts of my unknown friend who has developed this animation for schematic cross section of the ball mill presented here-

Schematic cross section of Ball mill in running condition

Considering the uniformity of desired particle size in ground slurry and energy consumption, single drum grinding mill having two compartments with rods and balls as grinding media in 1st and 2nd compartment has been found to be the best option as per recent studies. Thus, this system is the preferred choice for bauxite grinding for upcoming Alumina refineries in the World because it has the advantages in uniformity of product fineness as well as substantial reduction in electrical energy requirement by about 10 to 15% less compared to total electrical energy requirement in conventional single stage grinding system. The specific electrical power consumption for wet grinding in efficient system ranges from 4.6 to 4.8 kwh per tonne of bauxite.

It is, therefore, essential to evaluate all pros and cons of techno-economic features for all possible alternatives before taking final call to go ahead with the best suited option of grinding system meeting the process requirement with optimum energy consumption.
Kindly put your views / suggestions / remarks / comments, if any on the subject.

If you like this article, then please press your rating as  +1  .
Thanks and regards.

Kunwar Rajendra