Synthesis of Tri-octahedral Smectite

Abstract

Synthesis of tri-octahedral smectites such as hectorite, Mg-smectite, saponite, etc., was investigated for the purpose of industrial uses. They were synthesized according to the following procedure;(1) preparation of homogeneous Mg-Si precipitate from acidic Mg-Si solution, (2) washing and filtration of the Mg-Si precipitate to remove the secondary product, (3) slurry preparation from Mg-Si precipitate, NaOH, LiOH, HF, etc., (4) hydrothermal formation of smectite, and (5) drying and powdering of the product. X-ray powder diffraction patterns of the Mg-Si precipitate produced at room temperature show that this precipitate has low crystalline smectite-like structure
(Fig.1). This fact may be allow the formation of tri-octahedral smectites under relatively mild autoclaving conditions. The effects of temperature, time and concentration of Na, Li, Mg, Al and F, were examined.
Synthetic smectites were evaluated. Synthetic smectites were evaluated in comparison with Laponite, synthetic hectorite, and a purified bentonite product by methylene blue adsorption (MB), transparency (Trans), Hunter whiteness (WH), apparrent viscosity (AV), plastic viscosity (PV), yield value (YV) and gel strength (GS). The properties of representative synthetic smectites are as follows: hectorite (Si-Mg-Li-Na=8-5.4-0.6-0.7, 200°C, 2hr); MB=92m.equi./100g, Trans=89%(1% solu.), HW=96.4, AV=19cp (2.5% solu.), PV=10cp (2.5% solu.), YV=17 lb/100ft² (2.5% solu.), GS=13 1b/100ft² (2.5 % solu., after 10min.), hectorite (Si-Mg-Li-Na-F=8-5.4-0.6-0.7-3, 150°C 2hr); MB=96m. equi./100g, Trans=98%, HW=96.4, AV=34cp, PV=6cp, YV=55 lb/100ft ², GS=104 1b/100ft ², Mg-smectite (Si-Mg-Na-F=8-6-0.7-3, 200°C, 3 hr); MB=96m. equi./100g, AV=23cp, PV=6cp, YV=33 lb/100ft ², GS=88 lb/ 100ft ², saponite (Si-Al-Mg-Na-F=7.4-0.6-6-0.7-2, 300°C, 3hr); MB=104m. equi./100g, AV=17cp, PV=7cp, YV=18 1b/100ft ², GS=40 1b/100ft ².