The invention relates to a method for removing heavy metal ions from the lattice of tectosilicates or phyllosilicates, especially from zeolite mineral, particularly clinoptilolite, by exchanging ions with calcium ions. According to the inventive method, the zeolite rock is brought in contact with hydrochloric and ammonium-containing solutions in a chain of exchange reactors such that a large part of the cations of the lattice are replaced with ammonium ions, and the ammonium ions located in the lattice are replaced with calcium in a basic calcium hydroxide solution. The ammonium or ammonia used in the process is conducted in the circuit by binding the same in hydrochloric acid as an ammonium ion from the exchange solutions by conveying anhydrous ammonia and can be fed back to the exchange solution. The ions from the lattice that are exchanged are essentially precipitated as phosphate, carbonate, or hydroxide.