Adsorption and Desorption Kinetics and Equilibrium of Calcium Lignosulfonate on Dolomite Porous Media Baojun Bai,* ,† Yongfu Wu, † and Reid B. Grigg ‡ Department of Geological Sciences and Engineering, Missouri UniVersity of Science and Technology, 129 McNutt Hall, 1400 North Bishop AVenue, Rolla, Missouri 65409, and New Mexico Petroleum RecoVery Research Center, New Mexico Institute of Mining and Technology, 801 Leroy Place, Socorro, New Mexico 87801 ReceiVed: March 29, 2009; ReVised Manuscript ReceiVed: May 31, 2009 Calcium lignosulfonate (CLS) adsorption and desorption on a porous dolomite rock have been studied. Kinetic results showed that both adsorption and desorption are time-dependent processes, not instant. It has been found that adsorption and desorption have a two-step pattern: a fast adsorption/desorption followed by a slow step. Apparent adsorption and desorption rate constants were calculated by a second-order kinetic model. Desorption is an unequilibrated process under normal injection flow rate, and it is much slower than adsorption. Equilibrium results show that adsorption and desorption of CLS onto dolomite can be well fitted by the Freundlich equation over the experimental CLS concentration range and that increase of CLS concentration increases adsorption density. Increasing temperature slightly decreases CLS equilibrium adsorption. Increase of NaCl and CaCl 2 concentrations in brine increases adsorption density, but CaCl 2 has a much stronger effect than NaCl on the adsorption. Introduction Surfactants have been widely used to enhance oil recovery (EOR) in the oil industry, such as surfactant/micellar flooding, surfactant/alkaline/polymer (ASP) flooding, foam flooding, and surfactant huff-n-puff treatments. However, the costs due to their adsorption loss onto reservoir rocks often exclude the application of those EOR methods in oilfields. 1-4 Previous experiments have found that lignosulfonate, a paper industry waste, can be used as a sacrificial agent or a cosurfactant to significantly reduce the expensive primary surfactant adsorption on reservoir rocks. Neale and co-workers described the characteristics of lignosul- fonates and their importance to petroleum recovery operations. 5 Kalfoglou first reported in 1977 the use of lignosulfonate as a sacrificial agent to reduce the primary surfactant adsorption and found that lignosulfonate reduced the primary surfactant’s adsorption on crushed limestone rock samples by 16-35%. 2 Hong and co-workers evaluated lignosulfonate as a sacrificial agent for a surfactant flooding field test in a Glenn Pool reservoir, and their laboratory tests showed that the lignosul- fonate could reduce the primary surfactant adsorption by 39%. 6,7 Grigg co-workers 8-12 and Syahputra et al. 13 demonstrated that lignosulfonate could reduce the adsorption of the primary foaming agent CD1045 by 24-60% in Berea sandstone core and 15-29% in Indiana limestone core samples. Both adsorption equilibrium and kinetics are important to properly understand the interactions between chemicals and reservoir rocks and to optimize chemical process for chemical EOR applications. Equilibrium data provide the information of chemical adsorption on rocks, and kinetic data are related especially to the rate of adsorption. Previous publications for lignosulfonate onto different rocks mainly focus on the adsorp- tion equilibrium data, while few have been found in the literature on the kinetics of lignosulfonate adsorption. In fact, chemical adsorption on reservoir rocks usually takes a few days and even quite a few weeks to reach equilibrium. 14-18 Research of the adsorption and desorption rates will enable us to understand the mechanisms responsible for surfactant transport through reservoirs and to optimize cost-effective injection strategies for field application. Moreover, surfactant injection is often followed by water or other fluid injection, so it is of major importance to understand surfactant desorption processes. Nowadays, very limited results about lignosulfonate desorption kinetics have been published. Sandstone, limestone, and dolomite are three major types of reservoir rock. The authors previously reported the kinetics and equilibrium data of calcium lignosulfonate adsorption and desorption onto limestone and Berea sandstone. 8-12 This paper presents the kinetics and equilibrium of calcium lignosulfonate adsorption and desorption onto dolomite. Experimental Section Materials. Brine. Synthetic brine (2.0 wt %) was used in each test unless otherwise stated. The brine was composed of 1.5 wt % NaCl and 0.5 wt % CaCl 2 . Lignosulfonate. The lignosulfonate used in this study is Lignosite 100 calcium lignosulfonate (CLS), obtained from the Georgia-Pacific Corporation. The product is a powder produced by sulfonation of softwood lignin. Its basic properties provided by the Georgia-Pacific Corporation are listed in Table 1. Cores. Quarried Lockport dolomite was used in the study. The dolomite is mainly composed of CaMg(CO 3 ) 2 , and its properties and parameters are shown in Table 2. Experiments. Method for Analyzing Lignosulfonate Con- centration. Lignosite 100 sample was dissolved in distilled water for purification. After stirring overnight, the water-soluble samples were completely dissolved in the water except for insoluble impurities. After standby for about 1 week, the water solution was filtrated to remove all insoluble impurities. The * Author to whom correspondence should be addressed. E-mail: baib@ mst.edu. † Missouri University of Science and Technology. ‡ New Mexico Institute of Mining and Technology. J. Phys. Chem. C 2009, 113, 13772–13779 13772 10.1021/jp9028326 CCC: $40.75  2009 American Chemical Society Published on Web 07/02/2009