Pitch detackification with natural and modified talcs

Abstract

Pitch deposition in the pulp or in different parts of the manufacturing system can lead to a decrease in the quality of the final paper produced and to manufacturing efficiency problems. Tackiness is the property of pitch which related to the deposit formation. One of the methods to control pitch deposition in the pulp and paper industry is the use of the talc. The talc acts primarily by a detackification mechanism and hence must be part of the deposit to control further deposition. The effectiveness of talc as control agent depends on its structural and surface characteristics, e.g. specific surface, surface energy, surface charge and ratio lypophilic/hydrophilic surface, being these related to its mineral composition and the thermal and surface treatments it has undergone. Five commercial talcs, corresponding to two groups of different mineralogical compositions, have been tested to determine their detackification capacity using the deposition tester developed by the Complutense University of Madrid. In this method, the quantification of the deposits is carried out by an image analysis (IA) of stainless steel collectors on which the deposit has formed. After IA a qualitative analysis to determine the deposit organic fraction is carried out by gas chromatography (CG) after deposit extraction. The detackification capacity is expressed as the reduction of the deposits formed on the collectors when the different talcs at several concentrations are added to the pulp suspensions. The results show that pitch detackiness by talc addition is related to talc concentration and surface properties of mineral, as for example chlorite proportion, surface area and surface treatment and to the adsorption capacity of pitch on talcs. The general conclusions are that the talc having the highest quantity of mineral talc presents the best detackification capability and that all talcs studied have an appreciable detackification reduction at low proportion of addition.