Naturally occurring clays typically are mixtures of clay minerals and non-clay minerals, such as quartz, feldspar, carbonates, metal oxides and hydroxides.The use of particular clays often depends on their mineralogical composition, because the presence of some non-clay minerals may change few physicochemical properties and influence the purification of clay minerals. Carbonates and iron containing compounds behave as cementing agents, thereby inducing the aggregation of clay particles. Because of these aggregates the stability of clay suspensions decreases and the purification of raw clay samples from non-clay minerals is hindered. The aim of this study was to evaluate the changes in the aggregation and size distribution of clay particles and the stability of clay-water suspensions after complete or partial removal of carbonates with different organic acids. The influence of acid treatment on the dissolution of iron containing compounds was also investigated. The clay samples were taken from deposits in Latvia, containing 13-15% carbonates and illite as the main clay mineral. The influence on the aggregation and size distribution of clay particles depends on the type and concentration of the acids. Both calcite and dolomite is completely dissolved only in 0.2 M acids. Dissolution of iron compounds increases with increasing the concentration of acids.