Cross-flow leaching of alkali and alkaline-earth metals from sawdust and wheat straw – Modelling of the process

Abstract

Cross-flow washing of wheat straw and beech sawdust with water was carried out in order to leach the alkali and alkaline earth metals from them. Incremental concentration change (C = Δm/ΔV) of alkali and alkaline-earth metals in the leachate was plotted against the wash water volume. Maximum increase in Δm/ΔV was achieved after passing 0.04 to 0.06 dm3 of water through the washed biomass. After passing 0.2 dm3 of water through the biomass, leaching of alkali metals was practically completed. Concentration of potassium ion was predominant in the leachate. From the whole amount of alkali and alkaline-earth metal ions, found in the aqueous phase after washing, K+ ions make about 80% in case of wheat straw and 64% in case of beech sawdust. Concentration of other considered metal ions was much less comparing to the potassium ones.Change in the pH and electrical conductivity (EC) were measured after passing of each portion of wash water through the biomass. Change of the EC against the wash water volume follows fairly the change of leachate composition. Based on the experimental results, the process of alkali and alkaline-earth metals leaching was modelled assuming the cross-flow scheme of leaching process. Proposed model follows fairly the experimental data. Discrepancy between the experimental and calculated values for alkaline-earth metals in case of beech sawdust is attributed to a different leaching mechanism.