Ritsuro Miyawaki

Purification of Turkish sepiolite through hydrochloric acid treatment

Abstract Sedimentary sepiolite (Mg 8 Si 12 O 30 (OH) 4 (H 2 O) 4 ·8H 2 O) accompanied by dolomite (CaMg(CO 3 ) 2 ) from Turkey was purified with hydrochloric acid. The elution of magnesium from sepiolite resulted in decomposition of sepiolite and formation of amorphous silica when the rate of acid addition was not controlled, because rapid lowering of the pH of the sample slurry causes competitive reactions of hydrochloric acid with dolomite and sepiolite. However, sepiolite could be successfully purified by the controlled addition of hydrochloric acid to a sample dispersed in a 0.1M MgCl 2 solution. The purification is most effective if the pH of the sample slurry is kept higher than 6, a condition in agreement with the solubility diagram of sepiolite and dolomite. The sepiolite content was elevated from 47 to 92 wt%, and the dolomite content reduced from 52 to less than 1 wt%. Sepiolite is only slightly affected by this treatment as evidenced with XRD, DTA-TG, IR, N 2 adsorption and TEM.

Chapter 108 Crystal structures of rare earth minerals

Publisher Summary The rare earth minerals are defined as minerals containing rare earth elements as essential constituents. However, to judge this criterion, it is necessary to obtain structural as well as compositional information about the mineral. In addition, the determination of a chemical formula for a mineral also requires structural information in many cases, because the order or disorder of certain atoms in the crystal structure cannot be determined by chemical analysis alone. Therefore, minerals with significant contents of rare earths are treated as rare earth minerals in this chapter, even if the rare earth content appears “unessential” to the mineral. The rare earth minerals always contain a variety of rare earth elements. Crystal structures have been reported for about half of the known rare earth minerals. The structure analyses have revealed that many of them are solid solutions of the rare earth ions and other heterovalent ions that have ionic radii comparable to those of the rare earth ions; some of the rare earth minerals have independent crystallographic sites for rare earth atoms.