Supercritical Carbonation for Stabilisation and Reuse of Hazardous Wastes

超临界碳化已被确定为一种处理空气污染控制(APC)残留物的创新技术，APC残留物是一种特别麻烦的危险废物。经过处理后，它们可以安全地处置或重新用作建筑材料中的人造骨料。与其他可用的技术相反，该技术将粉状残留物转化为固体块，同时还以最小的能量输入固定重金属。另一个好处是，该过程捕获了地质上稳定的二氧化碳。该项目的目的是开发一种商业上可行的碳化APC残留物的方法，降低废物管理公司的处置成本，并为建筑业生产可销售的产品。废物能源(EFW)设施是越来越受欢迎的废物管理选择。然而，捕获产生的排放物会产生APC残留物，这些残留物被归类为危险物质。这些对环境的关注使得可接受的废物管理战略势在必行。然而，到目前为止，合适的治疗方法有限。加速碳化已被提出作为APC残留物的一种处理方法，粉末材料的碳化在几小时或几天内就能实现。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，加速碳化仍有缺点，即碳化不完全，产物呈粉末状或颗粒状，反应动力学较慢。然而，超临界碳化技术将提供加速、亚临界碳化的所有好处，同时也克服了其局限性。碳化作用将中和和固化粉状废物，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，该过程还将二氧化碳以地质上稳定的化学形式固定在稳定的残留物中。在78.1atm和31oC时，二氧化碳变得超临界，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大小毛孔的能力相结合，确保了快速碳化。此外，虽然采用传统的碳化方法，起始和最终产品都是粉末状或颗粒状，但超临界二氧化碳穿透小孔的能力使整体式样品能够得到处理，从而克服了与处理细粉相关的问题。通过改变石灰基固体的固液比，即APC残留物，可以控制固体的孔隙率，高比率可提供更大的孔隙率。超临界碳化是一种成熟的技术，已被证明改善了许多富钙材料的技术性能，减少了孔隙率，并增加了与碳酸盐物种填充孔洞相关的强度。然而，这项技术以前从未被用于处理废物，特别是APC残留物。使用超临界碳化技术稳定和固化APC残渣将提供一种具有成本效益的方法来处理这些麻烦的废物。这种方法的好处是：1。将碱性细粉转化为中性固体块体。比加速碳化更快速、更广泛的碳化。固定APC残留物中存在的重金属，特别是铅和锌，使其成为不溶性碳酸盐。除了水和二氧化碳(CO2)外，不需要额外的材料。不需要较高的温度，因此是一种能量相对较低的方法。我们确定了两条进入市场的商业途径：避免堆填区和生产替代建筑材料。我们正在与多家公司合作，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.