SORPTION OF ARSENIC ONTO LATERITE- A NEW TECHNOLOGY FOR FILTERING RURAL WATER

An arsenic filter was developed that uses laterite iron concretions to remove arsenic. The goal was to make an arsenic-iron removal system for less developed countries that costs little to operate, and is fabricated with locally obtained supplies. Laterite from Ghana and Brazil, which ranges in composition from 29 to 50% Si02, 24 to 40% Fe203, and 12 to 17% A1203,0.5 to 3% MnO2 was studied by means of column experiments. Sorption capacity for 2 mm grains is about 300 bed volumes of 1 ppm arsenic water. Contact times of 10 to 15 minutes reduce arsenic concentrations by about a factor of 100 to 1000, which allows the fabrication of fast-flow filters. Iron sorption was observed during our first field tests. Sorption capacity is > 200 bed volumes for five ppm Fe solutions. A 20-liter bucket filter, 100-liter bucket filter and two, meter-size filters that directly treat hand-pumped well water were field tested in Ghana. Laterite was hand-crushed, sized with window screen, and washed. Inclusion of abundant fines increases the arsenic sorption capacity. There was no indication that high silica tropical waters poison the filter. Bucket-filters comprising a plastic bucket, piece of window screen, laterite and board have flow rates about 0.5 to 1 liter/min. Laterite filters remove turbidity and off-tastes from drinking water and do not impart any new taste, hence the product water is readily accepted for drinking. Gravity-flow pump-filters made with cement blocks, window screen, and PVC pipe are at present being tested over a year's time and the results will be presented.

CORRESPONDING AUTHOR: David I Norman., Department of Earth and Environmental Science, New Mexico Tech, Socorro, New Mexico 87801, USA, email: dnorman@nmt.edu