Methods for minimizing unaccounted soda loss in Alumina refinery

Hi Friends,

We are aware that caustic soda is the basic input material used for dissolution of alumina present in bauxite for production of calcined alumina in Alumina refinery. In present post, we will briefly discuss one of the critical issues for operative Alumina refineries.

The specific consumption of caustic soda per tonne of alumina production is generally termed as overall soda loss in Alumina refinery which is ascertained on the basis of plant inventory carried out twice or thrice every month. The plant inventory is based on volumetric measurement of process liquor / slurry and analysis of collected samples to arrive at total production during the period and consumption of input raw materials.  Accounting of total soda loss is further assessed by estimating the consumption / losses under following sub-heads:

• Chemical soda loss,
• Soda loss with products,
• Soda loss with bauxite residue and
• Unaccounted or physical soda loss.

Caustic losses under first three subheads are estimated based on analysis and systematic calculations. But the difference of total soda loss and losses accounted under first subheads is indicated as unaccounted soda loss. At times, it becomes very difficult to technically justify the abnormally high figure on account of  unaccounted soda loss. The abnormally high figure has always bothered me to investigate this issue by tracking all possible factors so as to minimize the losses on this count in particular. I would like to share my personal experience in this regard. 

The specific unaccounted soda loss works out to around 3 to 4 kg per tonne of calcined alumina depending plant capacity. For bigger capacity plants, the figure is on the lower side, however, it may be little higher for smaller capacity alumina plants because of volume effect. In simple words, unaccounted soda loss means physical losses of soda from the plant through unknown sources. Following steps will contribute in reducing the unaccountable soda loss in Alumina refinery are outlined below-

1. Ensure correct receipt of fresh caustic lye in tankers received by rail or road,
2. Avoid accumulation of liquor on floors and immediate repair / steel cladding of drains and sump tanks minimizing seepage of caustic liquor to ground,
3. Recycling the washing of sample bottles and laboratory equipment to process circuit,
4. Ensuring no overflowing of process vessels and spillages of plant liquor outside process areas.

These are the main steps which will contribute in reduction of unaccounted soda loss significantly. Each individual must be vigilant to take care of these factors in Alumina refinery seriously and sincerely for minimizing unaccounted losses.

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Thanks and regards.

Kunwar Rajendra