Supercritical Carbonation for Stabilisation and Reuse of Hazardous Wastes

超临界碳化已被确定为处理空气污染控制（APC）残留物的一种创新技术，这是一类特别棘手的危险废物。经过处理后，它们可以被安全处置或作为建筑材料中的人工集料重新使用。与现有的其他技术相反，该技术将粉末状残留物转化为固体块，同时以最小的能量输入固定重金属。另一个好处是，这个过程以一种地质稳定的形式捕获二氧化碳。该项目的目的是开发一种商业上可行的方法，使APC残留物碳化，减少废物管理公司的处理费用，并为建筑工业生产一种可销售的产品。废物发电设施是越来越受欢迎的废物管理选择。然而，捕获所产生的排放物产生的APC残留物被归类为有害物质。这些环境问题使得制定可接受的废物管理战略势在必行。然而，迄今为止，合适的治疗方法有限。加速碳化已被提出作为APC残留物的处理方法，在数小时或数天内实现粉末状材料的碳化。地质上稳定的碳酸盐的形成已被证明可以固定许多有问题的重金属，包括铅和锌。然而，加速碳化仍然有缺点，即不完全碳化，粉末状或颗粒状的产物和反应动力学缓慢。然而，超临界碳化技术将提供加速、亚临界碳化的所有优点，同时也克服了其局限性。碳化将中和和固化粉末状废物，同时将许多环境问题的关键成分固定为稳定的碳酸盐。更重要的是，这一过程还将二氧化碳以一种地质稳定的化学形式固定在稳定的残留物中。在78.1大气压和31摄氏度时，二氧化碳变成超临界，具有液体的密度，但具有气体的渗透性。高气体密度和渗透亚微米级孔隙的能力相结合，确保了快速碳化。此外，虽然传统碳化的起始和最终产物都是粉末状或粒状的，但超临界二氧化碳穿透小孔隙的能力使整体样品能够被处理，克服了与处理细粉末相关的问题。通过改变石灰基固体（即APC残留物）的固液比，可以控制固体的孔隙度，高的固液比会产生更大的孔隙度。超临界碳化是一项成熟的技术，已被证明可以改善许多富钙材料的技术性能，通过碳酸盐物质填充孔隙，可以降低孔隙率，提高强度。然而，这项技术以前从未应用于处理废物，特别是APC残留物。利用超临界碳化技术稳定和固化APC废渣将为处理这些麻烦的废物提供一种经济有效的方法。这种方法的好处是：1。碱性细粉向中性固体块的转化。比加速碳化更迅速和广泛的碳化作用。3 .固定化APC残留物中的重金属，特别是铅和锌，作为不溶性碳酸盐。除水和二氧化碳（CO2）外，不需要其他材料。不需要高温，因此是一种相对低能耗的方法。用化学方法将二氧化碳固定在稳定块内。我们已经确定了两条商业路线；避免堆填和生产替代建筑材料。我们正与多家公司合作，以实现这些目标。

Supercritical carbonation has been identified as an innovative technique to treat air pollution control (APC) residues, a particularly troublesome class of hazardous wastes. Treatment enables them to be either safely disposed of or re-used as artificial aggregates in building materials. Contrary to other technologies available, the technique converts the powdered residues to a solid block whilst also immobilising heavy metals with minimal energy input. An additional benefit is that the process captures carbon dioxide in a geologically stable form. The purpose of this project is to develop a commercially viable method for the carbonation of APC residues, reducing the costs of disposal for waste management companies and generating a saleable product for the construction industry. Energy from waste (EfW) facilities are an increasingly favoured Waste Management option. However, trapping of the resultant emissions produces APC residues which are classed as hazardous materials. These environmental concerns make an acceptable waste management strategy imperative. However, to date, suitable treatment methods are limited. Accelerated carbonation has been proposed as a treatment method for APC residues, with carbonation of a powdered material being achieved in a matter of hours or days. The formation of geologically stable carbonates has been shown to immobilise many of the problematic heavy metals, including lead and zinc. However, accelerated carbonation still has drawbacks, namely incomplete carbonation, a powdered or granular product and slow reaction kinetics. Super-critical carbonation technology however will provide all of the benefits of accelerated, sub-critical, carbonation, whilst also overcoming its limitations. Carbonation will neutralise and solidify the powdered wastes, whilst immobilising many of the key components of environmental concern as stable carbonates. What's more, the process also immobilises carbon dioxide in a geologically stable chemical form within the stabilised residues. At 78.1 atm and 31oC carbon dioxide becomes supercritical, having the density of a liquid, but the permeability of a gas. The combination of high gas density and ability to permeate sub-micron sized pores ensures rapid carbonation. Furthermore, whilst with conventional carbonation both the starting and end products are powdered or granular, the ability of supercritical CO2 to penetrate small pores enables monolithic samples to be treated, overcoming problems associated with the handling of fine powders. By varying the solid-liquid ratio of a lime-based solid, i.e. APC residues, it is possible to control the solid's porosity, with high ratios giving greater porosity.Super-critical carbonation is a proven technology, having been shown to improve the technical properties of many calcium-rich materials, with reduced porosity and increased strength associated with the pore filling by carbonate species. The technology however has never previously been applied to the treatment of waste materials, in particular APC residues. The use of super-critical carbonation technology for the stabilisation and solidification of APC residues will provide a cost-effective means of treating these troublesome wastes. The benefits of this approach are;1. The conversion of an alkaline fine powder to a neutral solid block.2. More rapid and extensive carbonation than accelerated carbonation.3. Immobilisation of the heavy metals present in APC residues, particularly lead and zinc, as insoluble carbonates.4. Requires no additional material other than water and carbon dioxide (CO2).5. Does not require high temperatures and so is a relatively low energy approach.6. Chemically binds carbon dioxide within the stabilised blocks.We have identified two commercial routes to market; avoidance of landfill and the production of alternative construction materials. We are working with a number of companies to realise these aims.