Plessis Pieter W Du, Ojumu Tunde V, Petrik Leslie F
Department of Chemical Engineering, Cape Peninsula University of Technology, Keizersgracht and Tennant street, Cape Town, 8000, South Africa.
Environmental and Nano Science Research Group, Department of Chemistry, University of the Western Cape, Private Bag X17, Bellville 7535, South Africa.
Materials (Basel). 2013 Apr 29;6(5):1688-1703. doi: 10.3390/ma6051688.
Production of a high value zeolite from fly ash has been shown to be an avenue for the utilization of South African fly ash which presently constitutes a huge disposal problem. The synthesis of zeolites Na-P1 and analcime on a micro-scale has been successful and preliminary investigation shows that scale-up synthesis is promising. However, the post-synthesis supernatant waste generated contains high levels of NaOH that may constitute a secondary disposal problem. A waste minimization protocol was developed to reduce the volume of waste generated with a view to enhancing the feasibility of the scale synthesis. Series of experiments were conducted in 100 mL jacketed batch reactors. Fly ash was reacted with 5 Mol NaOH on a 1:1 mass basis during the aging step, followed by hydrothermal treatment in which ultrapure water was added to the slurry. This study shows that by re-introducing the supernatant waste into the experiments in such a way that it supplies the required reagent (NaOH) for the zeolite synthesis, zeolite Na-P1 and analcime can be synthesized. It also shows that the synthesis process can be altered to allow up to 100% re-use of the supernatant waste to yield high value zeolitic products. This study effectively constructed two protocols for the minimization of waste generated during the synthesis of zeolites from South African coal fly ash. This result could be used to establish a basis for legal and environmental aspects involved in the commission of a full-scale plant synthesizing zeolites NaP1 and analcime.
利用南非粉煤灰生产高价值沸石已被证明是解决目前粉煤灰处置难题的一条途径。在微观尺度上成功合成了Na-P1沸石和方沸石，初步研究表明放大合成具有前景。然而，合成后产生的上清液废料含有高浓度的氢氧化钠，这可能构成二次处置问题。为了提高放大合成的可行性，制定了一个减少废料量的方案。在100 mL夹套间歇式反应器中进行了一系列实验。在老化步骤中，粉煤灰与5摩尔的氢氧化钠按1:1的质量比反应，随后进行水热处理，向浆液中加入超纯水。本研究表明，通过将上清液废料重新引入实验，使其为沸石合成提供所需的试剂（氢氧化钠），可以合成Na-P1沸石和方沸石。研究还表明，可以改变合成工艺，使上清液废料的再利用率高达100%，从而生产出高价值的沸石产品。本研究有效地构建了两个减少南非煤粉煤灰合成沸石过程中废料产生的方案。这一结果可为建立大规模合成NaP1沸石和方沸石工厂所涉及的法律和环境方面的基础提供依据。
