AbstractThe adsorption of calcium ions from aqueous solutions on − 65 + 200 mesh quartz has been measured using Ca45as a tracer. Results are given for initial Ca++ion concentrations of (4.2 to 11.5) × 10−4gm. ions/liter over the pH range 4 to 12. Changes in pH occurring during the adsorption have also been determined. The mechanisms of cationic adsorption on quartz in aqueous media, and the activation of quartz surfaces for flotation with anionic collectors are critically discu