Simultaneous ammonium and phosphate removal by metal inorganic salt modification of natural zeolite

Abstract

Nutrients discharge into receiving waters can cause an environmental problem capable of deathly altering ecosystems. Natural zeolites are low cost resources with ion exchange capacity that have been widely studied. This study deals with simultaneous adsorption of nutrients; viz. ammonium and phosphate, onto different modifications of natural zeolite, clinoptilolite. Research has been focused on the optimization of surface modification procedures to raise clinoptilolite efficiency and to enhance the capability of regeneration. Four columns were filled with approximate 12 grams of zeolitic material; namely, natural nontreated (Z-N), manganese-modified (Z-Mn), iron-modified (Z-Fe) and aluminium-modified (ZAl) clinoptilolite. During three cycles, both adsorption and removal rate were investigated to evaluate clinoptilolite capacity loss. 􀂃 For adsorption studies influent was synthetic wastewater (4 L of loading solution containing 100 and 10 ppm of NH4 + and PO4 3-, respectively). 􀂃 For desorption studies influent was basic solution (1 L of 0,05 M of NaOH). On one hand, ammonium analyses reported similar results for each tested zeolite. Inorganic salt modification seemed not to increase clinoptilolite ammonium adsorption capacity. Generally, it was high during the first run. However, better ammonium removal from the influent was observed after column regeneration. Basic treatment probably activated the zeolite; thus enhancing first run results. Capacity results were in range of 9,0-16,0 mg NH4-N/ g of zeolite. Highest ammonium removal was reported of 0,2 g. On the other hand, phosphate analyses reported different results for each tested zeolite. Inorganic salt modification increased clinoptilolite phosphate adsorption capacity since natural clinoptilolite possess barely any selectivity towards phosphate ion. In general, phosphate adsorption was low, achieving a maximum removal of 10,1 mg adsorbed by Al-modified clinoptilolite. Two different mechanisms might rule over phosphate removal. Adsorption onto the zeolite framework was observed before basic treatment; and after, partial precipitation. This theory is buttress with low percentage of phosphate recovery during the regeneration, especially in Z-Al experiments. In 3rd cycle regeneration analyses, phosphate recovery percentage was 55%, 79% and 33% for the Mn-modified, Fe-modified, and Al-modified clinoptilolite. Global tendency is to guarantee water resources for supply and quality of water within aquatic systems. The proposed cost-effective technique promotes the recovery of nutrients, thus obtaining a potential fertilizer application very attractive to investors and stakeholders.