Formation and Phase Transformation of MgCO3?3H2O Whiskers in the Presence of Sodium Dodecyl Sulfate

Huge amounts of MgCl2 center dot 6H2O are produced annually as a byproduct or waste from KCl production in the Qinghai province of China. An ecological and economic way to solve this problem is transforming the abandoned MgCl2 center dot 6H2O to valuable MgCO3 center dot 3H2O whiskers. The formation and phase transformation of MgCO3 center dot 3H2O whiskers were studied in the crystallization process, in which MgCl2 and NH4HCO3 were precipitated in the presence of sodium dodecyl sulfate (SDS) at 50 degrees C. Results showed that porous spherical MgCO3 center dot 3H2O, MgCO3 center dot 3H2O whiskers, and flocculent rod-like 4MgCO3 center dot Mg(OH)2 center dot 4H2O were formed with decreasing concentration of SDS as the crystallization proceeded. When the concentration of SDS was lower than the critical micellar concentration (6.5 mmol center dot L-1) at 60 min, SDS was beneficial for the growth in the [010] direction to form onedimensional MgCO3 center dot 3H2O whiskers with a high aspect ratio, good uniformity, and a smooth surface (length, 60-70 mu m; aspect ratio, 110-140).