Revisiting NH₄⁺–Na⁺ cation exchange selectivity on smectites: Implications for ammonium/ammonia distribution and speciation in icy planetesimals, Ceres, and Enceladus

Data for an experimental dataset for the cation exchange reaction of NH₄⁺ on Na smectites (montmorillonite and saponite) and the results of speciation modeling using the determined selectivity coefficients.