Removal of wood dyes from aqueous solutions by sorption on un-treated pine sawdust

Synthetic dyes are extensively used in industry for various applications among which is the preparation of dyed wood veneers. The discharge of effluents containing dyes is of great concern due to their toxicity, mutagenicity and carcinogenicity and causes serious environmental problems. In this work, the possibility of using un-treated pine (Pinus radiata) sawdust, a waste product from the wood industry, as biosorbent for the removal of wood dyes from wastewaters was investigated. The BET surface area of the material was 0.36 ± 0.01 m2/g and the point of zero charge 4.8. Batch adsorption experiments were performed at 25ºC, natural pH (5.1, 6.0, 6.2 for blue, black and red dyes, respectively), 100 rpm and initial dye concentration of 5 mg L-1 to analyze the effect of the adsorbent dose (5 or 10 g L-1) and contact time (up to equilibrium) on the adsorption percentage for three dyes (blue, red and black). The highest adsorption percentage was attained at 10 g L-1 for an equilibrium time of 48 h: 67 ± 2.46% for blue, 34.46 ± 0.34% for black and 29.93 ± 0.27% for red. The maximum adsorption capacity decreased in this order: blue, 0.374 ± 0.032 mg g-1; black, 0.183 ± 0.001 mg g-1 and red, 0.161 ± 0.002 mg g-1. Kinetic data were best fitted to the pseudo-second order model, which suggests a chemisorption process.