Synthesis of zeolite adsorbents by hydrothermal treatment of PFA wastes: Acomparative study

A comparative study has been undertaken into the synthesis of zeolite adsor bents from pulverised fuel ash materials obtained from Indonesian and UK co al-fired power plants. Characterised samples of each type of raw material were pre-concentrated by magnetic separation to remove any deleterious iron contamination, before b eing hydrothermally treated with caustic soda over a range of experimental conditions. Cation exchange capacity levels of reaction products were deter mined and X-ray diffraction techniques were used to identify the types of z eolites formed. A maximum CEC value of over 280meq/100g was obtained after treatment of the UK material, representing a ten-fold increase on the raw s ample, whereas over 350meg/100g was achieved with the two Indonesian PFA sa mples, compared with raw material values of around 18meq/100g. Zeolite HS w as found to be the dominant type present, particularly in products synthesi sed from the Indonesian materials, and types A and X were identified in som e products derived from the UK sample. In all cases, metastable zeolite R w as also evident. Maximum zeolite formation and corresponding CEC values wer e generally achieved at high temperatures and low solid/liquid ratios, whil e zeolite type and degree of crystallisation were found to be dependent on the reaction conditions and the mineralogy of the raw material particularly in terms of the relative concentrations of SiO2 and Al2O3. (C) 2000 Elsevi er Science Ltd. All rights reserved.