INTERFACIAL ELECTROCHEMISTRY OF GOETHITE (ALPHA-FEOOH) ESPECIALLY THE EFFECT OF CO2 CONTAMINATION

The surface charge density/pH function of goethite is shown to be very similar to the surface charge density/surface potential functions reported for mercury. This finding differs from all other reports and we attribute the difference to the experimental method. This paper describes a method of titrating oxide suspensions which reduces pH drifts and suspension and stirring effects to negligible values and also a method for effectively removing CO2 from oxide suspensions. When goethite which had been stored as a suspension in contact with air was titrated in N2-purged NaI solution the point of zero charge (pzc) was within the range found by previous workers, i.e. pH 8.75 and the σ/pH function did not resemble reported σ/ψ0 functions of mercury but when goethite from the same preparation was purged with N2 for 2 months and then titrated in N2-purged NaI the pzc was pH 9.3 and the σ/pH function did resemble the σ/ψ0 function of mercury. © 1979 Elsevier Sequoia S.A.