Spectroscopic study of heavy metals sorption on clinoptilolite

Sorption of heavy metal cations (Pb(II), Cr(III), Cd(II), Ni(II)) from aqueous solutions on natural Na-clinoptilolite was studied using atomic absorption spectrometry (AAS) and FT-IR spectroscopy. It was found that the sorption capacity of clinoptilolite decreases in the following order: Pb(II) (22,600 mg/kg), Cr(III) (21,200 mg/kg), Cd(II) (10,400 mg/kg) and Ni(II) (6,200 mg/kg). In the FT-IR spectra of the samples, in the region of pseudolattice vibrations (500–800 cm^–1), systematic changes connected with the type of cation and its concentration in the initial solution were observed. The proportions of ion exchange and chemisorption in the whole process of sorption were also estimated. It was found that the amount of cations sorbed on clinoptilolite depended on the concentrations and pH of the solutions used as well as on the contact time of zeolite-solution system. After 120 min of the reaction, despite the metal type, 90–100% of the total amount of cations were immobilized.     

Recovery of Plant Nutrients from Dilute Solutions of Human Urine and Preliminary Investigations on Pot Trials

Within the context of Ecological Sanitation (ECOSAN), human urine has been the subject of research and practice as a potential fertilizer in the recent years. Although quite a lot had been done with original undiluted urine with promising outcomes, not much appears in the literature which concentrates on dilute solutions of urine. This is important because unless waterless toilets are employed, urine will be diluted with flush water in actual use. In this work, dilute solutions of urine are investigated with emphasis on the recovery of plant nutrients. A natural zeolite namely clinoptilolite was loaded with nitrogen, phosphorus, and potassium as an indirect route of processing urine. The results have revealed that hydrolysis is completed in shorter times in dilute samples. Clinoptilolite could successfully remove plant nutrients from all dilute solutions. Nitrogen could be recovered up to 86% with higher efficiencies at higher concentrations in general. Recovery of orthophosphates increases with increasing concentration to reach 96%, however, potassium could not be recovered. The preliminary experiments with grass have revealed that nutrient loaded clinoptilolite was as effective as chemical fertilizers while direct application of original and diluted solutions of urine had shown inferior yields.     

Accumulation of acid sites on natural clinoptilolite under recurring dehydration

A new ¹H NMR approach was applied to study the influence of recurring dehydration on the acidity of a natural Ca-rich zeolite clinoptilolite. It has been found that thermal cycling progressively increases the rate of the proton exchange between water molecules in the rehydrated state. The observed effect is interpreted as a result of the irreversible accumulation of specific structural defects represented by Brønsted acid sites: each dehydration at 720 K adds to the acid sites in an amount of the order of 10^?3 per unit cell. The number of these defects, detected by NMR in hydrated mineral, is in reasonable agreement with their amount estimated for the dehydrated state with an IR-spectroscopy CO-probe method. A comparison of the results obtained for two distinct zeolite samples shows that the Ca²⁺ ions are of first importance in the dehydration-induced formation of the active acid sites. The barrier for the proton-transfer reaction between the acid sites and H₂O molecules in hydrated clinoptilolite is found to be 46 kJ mol^?1, which is not too different from the value of 54 kJ mol^?1 reported recently for natural chabazite.