Zeolites and zeolite rocks are commonly used in different industrial applications. Natural zeolites present an attractive material for environmental applications because of their high abundance, availability and low costs. Depending on geological settings and conditions during mineral formation, natural zeolite deposits usually represent a heterogeneous mixture of zeolite minerals together with varying amounts of gangue minerals (e. g. quartz, feldspars and phyllosilicates). Hence, profound mineralogical knowledge and a detailed characterization of natural zeolites are essential for tapping their full potential in any practical application. However, this is rarely done as detailed mineralogical characterizations are elaborate and often neglected in favour of bulk chemical analyses (e. g. XRF). In this paper we describe typical technical applications for natural zeolites as well as the requirements demanded for their use. An analytical protocol has been developed for the detailed characterization of natural zeolites for ammonium exchange consisting of a combination of mineralogical and chemical methods and is exemplarily demonstrated. The methodology comprises mineralogical investigations with X-ray diffraction (XRD) and electron microprobe analyses (EPMA) to provide qualitative data on mineral compositions and in-situ analysis of mineral chemistry (Si/Al-ratio, cation contents). The examinations are accompanied by bulk chemical analysis (XRF) as well as thermoanalytical investigations (TG/DSC) to distinguish between certain zeolite minerals. Finally, ion exchange experiments for ammonium have been carried out to determine the cation exchange capacity (CEC) of zeolite samples for a defined range of concentrations.The aim of the study is to develop an analytical routine in order to enable the detailed characterization of natural zeolite samples with standardized means of mineralogi-
The technical feasibility of an ammonium recovery process ('ion-exchanger-loop-stripping') for sludge liquor from municipal wastewater treatment plants is examined. The proposed process combines ion-exchange on natural zeolites with simultaneous air stripping of ammonia to produce an industrial NOx-removal agent. Column experiments with continuously recycled NHCl-solutions and a real sludge liquor sample were conducted to determine basic ion-exchange kinetics of the applied clinoptilolite. Mass balances of consecutive loading/regeneration cycles show the positive influence of NaCl-pretreatment as well as simultaneous air stripping on the NH-exchange capacities. Removal rates for NH between 61.5 and 84.6% were achieved at NH-concentrations typical for sludge liquor (900 to 2,300 mg L). Zeolite loadings ranged from 5 to 8 mg NH g after 90 min of loading. Regeneration rates were between 42.9 and 49.7%, but increased to 64.8% with simultaneous air stripping. A minimal decrease in the ammonium removal rate was observed as a result of matrix effects in sludge liquor (e.g. flocculants, competing ions). Liquid analyses showed a considerable phosphate-reduction in the sludge liquor sample after ion-exchange due to potential struvite or apatite precipitation. The obtained results enable a detailed design, scale-up and further optimization of the ion-exchanger-loop-stripping process in future.
Abstract:The paper quantifies the synergy-effects of an areal combination of biogas-plants with plants of the building materials industry (e.g. cement plants) from the energetic and economical point of view. Therefore a model biogas and cement plant are defined and the effects of a combination of both plants in terms of energetic efficiency, investment and operating costs, greenhouse gas emission reduction and overall energy production costs are quantified. The main benefits of this combination are the utilisation of low temperature excess heat sources from the cement plant for fermenter heating and the direct thermal utilisation of unprocessed biogas as a valuable, CO 2 -neutral fuel for combustion processes for instance clinker burning. Due to the combination, the energetic efficiency of the biogas plant, defined as utilisable energy output in relation to the energy content of the produced biogas, significantly increases from 63.0% to 83.8%. Concurrently the energy production costs are reduced, turning biogas into a competitive source of energy without the need for federal sponsorship. Calculations show, that from a plant size of around 90 m³ STP /h biogas production costs in combined plants are even lower than the actual market prize of natural gas.
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