A group of researchers including Dr A Sriram, S A Bhale, N P Nagmote and Dr A N Deshmukh have suggested that bauxite can be used as a defluoriding agent in the domestic water filters in place of the activated alumina, which is comparatively quite expensive. A research paper based on the study was recently presented at a national symposium on fluorosis control held here.

Defluoridation of drinking water, using domestic water filters, has been found to be by and large the most effective way to prevent excessive fluoride intake in the fluorosis endemic villages. There are two methods of defluoridation that are currently in use. One of them is known asNalgonda technique, under which calculated amount of alum, lime and bleaching water are added to the pretreated water and the mixture is agitated. Fluorides are absorbed by the aluminium hydroxide complexes and settle at the bottom of reactors.

However for optimum fluoride removal, alum and lime need to be added in certain proportions and a trained operator and chemist are required to operate this filter. As against this, the defluoridation plants based on activated alumina are very simple to operate and even the villagers themselves can handle the filters with some initial training. The only problem with the mass utilisation of these filters is that the cost of activated alumina is comparatively high at about Rs 130 per kg. The purpose of studying the role of bauxite as a cheaper substitute arises out of this high cost factor.

Under the study, about eight samples of bauxite from different ore deposits all over the country were tested and found to be suitable as cheaper substitute of activated alumina fordefluoridation of drinking water. The team has also found that after its use as medium for fluoride removal, bauxite still retains as ore of aluminium, with certain value addition. This fluoridated bauxite can be preferred for metallurgical purposes, since they will be more suitable for aluminium smelting.

The team has come up with comparative costs of using activated alumina and bauxite in the domestic water filters. For the purpose of testing and calculation, drinking water from fluororis-endemic Gadegaon Village of district Chandrapur containing about 5.70 mg of fluoride per litre was taken.

It was found that the cost of obtaining potable water (containing 1.5 mg per litre) at the rate of 25 litres per day from ground water containing 2.0, 3.0, 4.0 and 5.0 mg per litre of fluoride comes to about Rs 460.65, Rs 602.25, Rs 745.65 and Rs 888.00 respectively.

For the similar specifications, the use of bauxite as the defluoriding agent can lower the cost of filtering to Rs 81.93, Rs 245.80, Rs 426.06 andRs 581.00 respectively. Both the calculations are for a period of five years and considering use of three kgs of activated alumina and five kgs of bauxite. The paper mentions that the cost of defluoridation will be slightly higher, if treated (chemically active) bauxites are used.

The researchers have concluded that the use of bauxite as fluoride-removing medium is encouraging not merely because it can bring down the cost of defluoridation, but also on the account of the fact that bauxite is a natural resource, available in almost all regions of the country. Another point of great importance is that, there is no loss of this natural resource and the rejected bauxite from defluoridation units can be more effectively used for aluminium metallurgy.

The paper also mentions that for those villages where the ground water contains marginally excessive amounts of fluoride, the domestic defluoridation plants based with bauxite as fluoride-removing medium will be exceedingly cost-effective. It also mentions thatfor the present study only limited number of samples from all over country were taken up and more detailed study needs to be undertaken for the characterisation of those bauxite deposits in the country, which have potential for maximum fluoride-removal capability.

Also the study on fluoride removal capacity of Gibbsite, which constitutes more than half of Indian bauxite deposits, merits serious efforts, mentions the paper.