Cation‐Exchange Capacity and pH in the Coagulation Process

determination, employed by Langelier, Ludwig, and others and based on measurements of dried material, are scarcely applicable to the study of existing turbid waters, however. Therefore, a method for measuring the CEC of such dilute clay suspensions is needed. In the present study, the methylene blue method reported by Robertson and Ward,2 was modified in order to measure CEC and was found to be fairly simple and reproducible. Recently the use of the microscopic electrophoresis method of zeta potential measurement has been advocated by Pilipovich,3 Black,4 and Riddick5 as an important tool for coagulation study. Black and Hannah,6 Packham,7 and Stumm and Morgan 8 re-emphasized the importance of pH in coagulation, and Packham noted the lack of pH control in the 1949 work of Langelier and Ludwig. The results obtained by the above investigators indicate that further studies of the interrelationships of CEC, pH, and alkalinity are needed to aid in understanding and improving the coagulation process in water treatment. It has been the aim of the present study to pursue the earlier work of Langelier and Ludwig with the newer tools now available, such as a new m thod of CEC measurement, microelectrophoresis, and pH-controlled coagulation. As yet, there is no sufficient basis for determining what chemical treatment should be used or what coagulant aids should be added to a given raw-water suspension to produce the best coagulation at minimum cost. The present study is intended to aid in the development of such a basis.