REMOVAL OF METAL IONS FROM LEACHATE

Waste deposits generate polluted water, leachate, which contains metal ions. Leachate is often led to waste water purifying plants. The metals sediment and end up in the digested sludge, which often is taken back to the waste deposit. This results in a negative eco-cycle.

Metal ions in solution can be captured by ion-exchangers, but commercially available ion-exchangers are expensive. The aim of- our project was to investigate whether natural and renewable materials could be used as economical and environmental friendly ion-exchangers to capture metal ions in leachate before it enters the water purifying process.

Bark, lignin and wood (sawdust) are by-products from the forest and pulp and paper industry, that mainly are used as solid fuels. We have tried to produce natural ion-exchangers by treatment of wood, bark and lignin with ozone and/or alkali. The ion-exchanging capacity was investigated in a model solution with known concentrations of copper, iron and manganese. The concentrations of metal ions were determined by Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES).

The results showed that the natural materials treated with both ozone and alkali effectively captured metal ions in solution. However, we round that the ozone treatment probably was unnecessary. For example, wood treated only with alkali removed 90 % of the iron and > 99 % of the copper and manganese ions in the solution.

In conclusion, we have demonstrated that bark, lignin and wood can be used as natural ion-exchangers. These materials are by-products and their value as solid fuels would not be lost, because they could be dried and burnt after their use as ion-exchangers. Further studies are needed to establish whether this method could he used in practise and to evaluate the advantages/disadvantages in comparison to currently available methods for purification ot leachate. However, this method for removal of metal ions from a solution might be useful also for other purposes.