1218
FREDL. PUNDSACK AND GEORGE REIMSCHUSSEL
Vol. 60
THE PROPERTIES OF ASBESTOS. 111. BASICITY OF CHRYSOTILE SUSPENSIONS1 BY FRED L. PUNDSACK AND GEORGE REIMSCHUSSEL Contribution from the Johns-Manville Research Center, Manville, New Jersey Received February S& 1056
It is sho\m by means of conductivity and colorimetric analyses data that in aqueous suspensions hydroxyl and magnesium ions dissociate from the surface of chrysotile. Provided enough fiber surface is presented to the solution, an equilibrium comparable to that, attained by magnesium hydroxide is reached. The saturation concentration of magnesium hydroxide in equilibrium with eight different chrysotile specimens is determined as well as the solubility product constant for the fiber surfxc. The total basicity of chrysotile is evaluated, and the material is titrated stepwise with hydrochloric acid. The titration data are interpreted in terms of the structure of chrysotile.
Introduction It has been pointed out that in aqueous suspensions the hydrated magnesium silicate mineral chrysotile (Mge(OH)8Si4OI0)bears a marked resemblance to magnesium hydroxide.2 One purpose of the work reported here was to determine quiintitatively by means of conductivity measurements the degree to which magnesium and hydroxyl ions dissociated from the surface of chrysotile and to denionstrate the manner in which this effect was dependent upon the exposed surfaces. While this study has been limited to chrysotile, many of the arguments and conclusions apply to certain of the kaolin clay mineral group (A1,03.2Si0.2H20) which has been described as the aluminuni analog of chrysotile.3 I n coinmoii with most minerals, the composition of chrysotile varies from the ideal to a greater or lesser ext,ent depending upon the source of the sample. This is reflected by the fact that a t least three different varieties of chrysotile known as soft, semiharsh and harsh are recognized. Although the terms are somewhat ambiguous in that they refer to the"fee1" of the fiber when touched, in general, a soft fiber has a higher tensile strength and greater flexibility than a harsh fiber. It has been reported that t8heharsh fiber varieties have lower combined water contents than do tJhe soft ~ a r i e t i e s . I~n the current study it was felt that these differences in the propert,ies of various varieties of chrysotile might be reflect>edby the degrees of dissociation of hydroxyl and magnesium ions from the surfaces of the fibers. With this in mind chrysotile specimens from eight localities were examined for degree of surface dissociation to see if significant differences did occur. The basicit,y of chrysotile is demonstrated by the fact that the fiber reacts with acids, and if the acid is stiuig the fiber v i 1 1 react c,oinpletely tjo form a hyclrated silica resitfile. This has been recognized for a long tinie,b-7 but 110 detailed study of t'he cwirse of the reaction appears to have been made. This s n i w tJype of reaction occurs to differing extents with many members of the clay minerals (1) Preceding pit,per i n this series, F.L. Pundsacli, T H I SJ O U R N A L , 60, 301 (1050). ( 2 ) F. L. Piindsack, ibid.,59, 892 (1055). ( 3 ) 0 . \\'. Rrindley, "S-Ray Identificatiot~and Crystal Structure of ('1;i.v l l i n c i a l s . " Tlir: hli~iri.nlogicn1Society. 1,ondon. 1951. ( 1 ) \ I . s. l h d d l , ~ l ,7'?ri,,.. ( * , I , , . / , , , * I , . l / , u i , , v . I / ! / , , 54, I T > ! (lCI5l). .41~011., (;~iii,t,i,-Z., 4 1 , I X l i l i l ! l 2 7 j . I(;) I ) . \ \ ' < > l o , . l i < ~I 'n: i,i i i ~ ~ l i : i i i I':rtrut :{4U,!tOl ( . 4 l ) i i l l ! l : t l ) . ( 7 ) I , 1 1 . I'i
