Proceedings of the XV Balkan Mineral Processing Congress, Sozopol, Bulgaria, June 12 – 16, 2013 1245 EFFECT OF SODIUM POLY ACRYLIC ACID (NA-PAA) AS A DISPERSANT ON COLEMANITE Fırat KARAKAŞ, Ceren ERGÜNEŞ, Behzad VAZIRI HASSAS, Mehmet Sabri ÇELİK Istanbul Technical University, Faculty of Mines, Mineral Processing Engineering Department, 34469, Maslak, Istanbul, TURKEY ABSTRACT. Architectural waterborne paints consist of four main parts: solvents, pigments, binder, and additives. Various minerals, so-called pigments, should be well dispersed to obtain a homogenous film. This is why dispersion agents are widely used in such systems. One of the well-known dispersants used in paint industry is sodium salt of Poly Acrylic Acid (Na-PAA). Since Colemanite, a boron mineral, can be introduced in waterborne paints for a number of reasons; in this study adsorption behavior of Na-PAA and its interaction with colemanite mineral have been carried out. Electrokinetic, rheology and stability studies on colemanite suspensions with and without NaPAA have been studied in detail. Two different NaPAA polymers with the molecular weights of 2100 g/mol and 5100 g/mol have been used to ascertain the effect of molecular weight on adsorption and its associated properties. It is revealed that Na-PAA improves the stability and viscosity characteristics of colemanite suspensions which are favorable properties in paint. INTRODUCTION Paint is a composition which offers protection, coverage or texture to the substrate it is applied. While in structure it is composed of pigments or minerals, solvents, additives and relevant chemical agents, following the film formation only pigment particles are present within the web of binder polymers due to the solidification of the paint. As the homogenous distribution of the pigment particles on the binder polymer in dried paint film defines the quality of the paint, use of essential dispersants for the stabilization of the system becomes prominent. In general, the constitution of dispersing procedure affects the rheology and optical properties of the paint precisely, for which the homogeneously dispersed form of the pigments, must be prevented from re-agglomeration. Since the coagulation may occur spontaneously through London-Van der Waals attractive forces, the surface properties play a fundamental role on the stability of suspensions. Electrostatic repulsions (coulomb interaction) between similarly charged particles, repulsive non-DLVO forces arising from solvation of adsorbed layers, or most frequently by an electrosteric mechanism created by the use of polyelectrolyte are the forces to overcome the tendency to coalescence among particles (Fazio et al., 2008, Boisvert et al., 2001). In this study, the effects of NaPAA adsorption on the colemanite is investigated in terms of rheological, electrokinetics and stability. Two different NaPAA with different molecular weight were used to understand their effect on colemanite suspensions and corresponding paints. EXPERIMENTAL STUDIES Materials and Method Colemanite sample used in this study was obtained from “Eti Maden Bigadiç” concentrator with a maximum particle size of 25 mm and B2O3 grade of 40.97%. In consideration of the proper particle size that is applicable in paint production, the sample was enriched in a tumbling scrubber, upgrading its B2O3 content to 43.52% prior to grinding. After scrubbing, two steps of grinding are applied, being the first one with a ceramic ball mill to below 500µm, and second one with “Union Process” high speed attritor to a size range with d10, d50 and d90 sizes of 1.0 µm, 5.9 µm and 27.5 µm respectively. Dispersing agent, NaPAA (sodium salt of Polyacrylic acid), was acquired in powder form from Sigma-Aldrich Company with two different molecular weights of 2100 g/mol and 5100 g/mol. Water used in experimental studies was produced by distillation method. The conductivity value of distilled water was found as 1.4 µmhos.cm -1 . In addition, purity of water periodically controlled by total dissolved solids (TDS) equipment and the results of these measurements were found as 0 ppm during all tests. Characterization of Colemanite Colemanite is boron mineral with Ca 2+ cation in its lattice structure. Once colemanite hydrated, it experiences an acid-base reaction in the environs by minimum solubility which corresponds to its natural pH of 9.3 (Celik and Yasar, 1995). Since this dissolution of the Ca 2+ has strong effect on the characteristics of the suspensions containing colemanite, total dissolved solids (TDS) profile of this mineral suspensions in various solids % wt. was formed in order to determine the appropriate percent solids for each specification test, and required time for suspension to be stabilized, which is shown in Figure 1. Fig. 1 TDS Profile of Colemanite as a function of time As well as the type and charge of the adsorbent, the adsorption of polyelectrolytes onto the surfaces of solids strongly depends on the solution pH, the ionic strength, and the surface charge of solids (Liufu et al., 2005), in the case of Colemanite, however, due to the buffer behavior of the it, the pH of suspension does not shift to the acidic range and is always above 7 hence this parameter is not significant on adsorption. Moreover, Chen and coworkers reported the optimum dispersion in the pH range of 7–11, as they found the required NaPAA for desired dispersion in high pH values was lesser than that in acidic pH values (Chen et al. 2004). The viscosity measurements of the suspensions were done using “Brookfield DVII+” viscosimeter at 50 % solid wt. For the stability characteristics, the settlement pattern of the suspensions was inspected in glass cup holders with 10 ml volume at 10 % solid wt. Electrokinetics of the colemanite particles was conducted at 1 % solid wt., by “Zeta meter 3.0+” equipped with a microprocessor unit that automatically calculates the electrophoretic mobility of the particles, converting it to the zeta potential. RESULTS AND DISCUSSION Effect of NaPAA on Suspension Viscosity Viscosity measurements of the colemanite suspensions were performed at 50 % solid wt. in the presence of NaPAA with concentrations of 0, 500, 1000, 1500 and 2000 mg/L. Figure 2 and Figure 3 refer to the viscosity values of suspensions with addition of 2100 g/mol and 5100 g/mol NaPAA separately at different concentrations. Increase of NaPAA dosage results in a decrease on viscosity values of the system for 2100 g/mol and 5100 g/mol of NaPAA. 0 200 400 600 800 1000 1200 0 1 2 3 4 TDS, ppm Time (h) 0.1 1.0 5.0 Percent