Method and plant for synthetizing iron-free zeolites

Natural occurring material such as kaolin, clay, pumice, etc. containing Al2O3 and SiO2 and contaminated with Fe compounds are treated hydrothermally in a soda alkaline solution to dissolve the Al2O3 and SiO2 and give a residue containing the Fe compounds which are removed by filtration. The solution is used in a hydrothermal process to form crystalline zeolites. A plant or carrying out the process are described. Thus, an aq. 11% NaOH solution was used to treat pumice at 95 °C for 5 h. Afer been filtred the solution had the compound 1.27 SiO2 0.072 Al2O3 1.17 Na2O 5.6 H2O. The residue containing Fe was crystallized and readily adsorbed H2O. The compound of the filtrate was adjusted to that compatible with manufacturing zeolite A. After the adsorption material was treated at 105 °C for 5-7 h and crystallized zeolite A was obtained with a exchange capacity of 150 mg CaO/g zeolite after stirring the zeolite in a CaCl2 solution for 20 min. When the zeolite was placed in a Na perborate solution at 60 ° C for 20 min the perborate was 28 % decomposed.