The surface activities of SDS and mixture of SDS dodecyltriethylammonium bromide (DTEAB) in mineralized water were studied. It was shown that SDS has higher surface activity in mineralized water than in both deionized water and NaCl solution. This is because there exists strong interaction of Ca²⁺ or Mg²⁺ with SDS micelles and surface adsorption layer, furthermore, compared to SDS, the Krafft points of the mixture of sodium dodecylsulfate and calcium dodecylsulfate have no very distinct increment when plenty of Na⁺ exists. It was shown that the mixture of SDS and DTEAB has strong synergism in mineralized water, which is similar to those in both deionized water and NaCl solution. The results show that the mixture of cationic anionic surfactants has good ability of mineralized water tolerance. The synergism of mixed SDS DTEAB was explained in terms of strong electricity interaction between oppositely charged head groups of SDS and DTEAB.

Key words: SDS, mineralized water, surface activity, cationic-anionic surfactant combination