Correlation between the d-value and the M2+:M3+ cation ratio in Mg–Al–CO3 layered double hydroxides

• Published in: Applied clay science Vol. 130; pp. 2 - 11
• Main Authors: Zhitova, E.S., Krivovichev, S.V., Pekov, I.V., Yakovenchuk, V.N., Pakhomovsky, Ya.A.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.09.2016
• Subjects: d-Value; Hydrotalcite; LDHs; M2 +:M3 + ratio; Pyroaurite; Quintinite; LDHs; M2+:M3+ ratio; Hydrotalcite; d-Value; Quintinite; Pyroaurite
• ISSN: 0169-1317; 1872-9053
• DOI: 10.1016/j.clay.2016.01.031

Twenty-six samples of natural layered double hydroxides (LDHs: hydrotalcite, pyroaurite and quintinite) from various localities worldwide have been studied by means of single-crystal, powder X-ray diffraction and electron microprobe analysis. High crystallinity of samples allowed for the good accuracy of the measured d-values and reliable values of the M2+:M3+ ratios. Based on the obtained data, it has been found out that d-value for LDHs depends upon the M2+:M3+ ratio that can be explained by purely crystal chemical reasons. The ideal d-values for M2+:M3+=2:1 (quintinite group) and 3:1 (hydrotalcite group) are 7.56 and 7.80Å, respectively, whereas intermediate cation ratios correspond to the intermediate d-values. The observed quantitative correlation between d-value and M2+:M3+ cation ratio for carbonate LDHs can be described by the linear function d=0.2385×R+7.0852 (R=M2+:M3+), which allows for the estimation of M2+:M3+ on the basis of d-value and vice versa. [Display omitted] •Natural LDHs: quintinite, hydrotalcite, pyroaurite were studied by single-crystal and powder XRD.•The d-value was refined by single-crystal and powder data for Mg–Al–CO3 and Mg–Fe–CO3 natural LDHs.•d-Value increases with the increase of the M2+:M3+ ratio.•2:1 and 3:1 LDHs can be distinguished by XRD on the basis of d-value (mineral identification).•The provided equation allows M2+:M3+ ratio on the basis of d-value for CO3-bearing LDHs.