Formation and Phase Transformation of MgCO 3 ·3H 2 O Whiskers in the Presence of Sodium Dodecyl Sulfate.

Huge amounts of MgCl 2 ·6H 2 O 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 MgCl 2 ·6H 2 O to valuable MgCO 3 ·3H 2 O whiskers. The formation and phase transformation of MgCO 3 ·3H 2 O whiskers were studied in the crystallization process, in which MgCl 2 and NH 4 HCO 3 were precipitated in the presence of sodium dodecyl sulfate (SDS) at 50 °C. Results showed that porous spherical MgCO 3 ·3H 2 O, MgCO 3 ·3H 2 O whiskers, and flocculent rod-like 4MgCO 3 ·Mg(OH) 2 ·4H 2 O 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·L -1 ) at 60 min, SDS was beneficial for the growth in the [010] direction to form one-dimensional MgCO 3 ·3H 2 O whiskers with a high aspect ratio, good uniformity, and a smooth surface (length, 60-70 μm; aspect ratio, 110-140).