The effects of leather tannery sludge on the leachates from soil columns

Abstract

Leather tannery sludge from a chrome-tanning plant was added to the surface horizon of a typic haplustox from South Africa at rates equivalent to 0, 10 and 100 t ha⁻¹. Leaching columns were set up with 100 mm of the topsoil over 200 or 300 mm of subsoil material. The columns were watered intermittently and the leachates collected and analysed. The results show that, of the major cations, sodium leached fastest, followed by potassium and then magnesium and calcium. The anion analyses revealed that chloride predominated in the early leachates with nitrate and latterly sulphate becoming more important with increasing volumes of leachate. Moderate to high sodium absorption ratios of the leachate were counterbalanced by high electrical conductivity so that, for this soil, the use of such a sludge posed no real threat to either soil structure or groundwater quality; extrapolation to the field situation would require caution, however. It is probable that the recycling of chromium and washing of the sludge at the tannery to remove the sodium would enable such sludges to be used as soil amendments, especially on these strongly acid soils.