Abstract:

The influence of octaethylene glycol mono-n-hexadecyl ether (I) and SDS on the crystn. of Ca oxalate from 0.3 mol dm-3 NaCl solns. was investigated. The crit. micellar concn. (CMC) of I in H2O and 0.3 mol dm-3 NaCl was detd. by surface tension measurements (CMCH2O:CMCNaCl = 7.2.10-6 mol·dm-3). The kinetics of pptn. of Ca oxalate was followed by Coulter counter, and solid phases were characterized by polarized microscopy, thermal anal., and x-ray powder diffraction patterns. Under the pptn. conditions employed, the thermodynamically stable monohydrate, CaC2O4·H2O was the predominant cryst. form. In the presence of micellar solns. of I, pptn. of this phase was facilitated as evidenced by higher initial pptn. rates and higher ppt. vol. and no. of particles, as compared to the controls. Micellar solns. of SDS retarded pptn. but induced crystn. of Ca oxalate dihydrate, CaC2O4·(2+x)H2O (COD, x ≤ 0.5). Thus at c(SDS)\textgreaterCMC, the ppts. contained ≥85 mass % COD. The results were discussed in relation to previously reported data on the pptn. of Ca oxalate in the presence of dodecyl ammonium chloride. [on SciFinder(R)]