Reactive dyes removal from wastewaters by adsorption on eucalyptus bark: variables that define the process

An attempt to help solving the pollution problem caused by the presence of reactive dyes in textile effluents, was undertaken. Owing to the fact that eucalyptus bark is a very abundant, inexpensive, forest residue in the authorsʹ country, Portugal, it was decided to experiment with it as a potential adsorbent for a certain type of the supracited pollutants used in cellulose fibers dyeing (Remazol BB). In order to study the variables that define the process, 24 and 25 factorial experimentations were carried out, in two stages. In the first one, the variables selected were: temperature, initial pH, sodium chloride concentration and initial dye concentration/bark concentration ratio. As tests showed that the last parameter did not describe the adsorption process, another stage followed, keeping the first three variables and substituting initial dye concentration and bark concentration separately for their ratio. It was verified that all the variables studied had significant influence on the adsorption process at the level of 1% probability. The influence order was: initial dye concentration>bark concentration>initial pH>sodium chloride concentration>temperature. Parallel adsorption tests, under similar conditions, carried out with a commercial activated carbon and with eucalyptus bark, showed for the last one an adsorption capacity about half of that of the first one. It is considered that the obtained results are quite encouraging, though there is still a long way to go before definitive conclusions may be withdrawn.