Laursen Karin, Kern Arnt A, Grace John R, Lim C Jim
Pulp and Paper Centre, University of British Columbia, Vancouver, Canada.
Environ Sci Technol. 2003 Aug 15;37(16):3709-15. doi: 10.1021/es026090k.
It has been known for a long time that certain additives (e.g., NaCl, CaCl2, Na2CO3, Fe2O3) can increase the sulfur dioxide capture-capacity of limestones. In a recent study we demonstrated that very small amounts of Na2CO3 can be very beneficial for producing sorbents of very high sorption capacities. This paper explores what contributes to these significant increases. Mercury porosimetry measurements of calcined limestone samples reveal a change in the pore-size from 0.04-0.2 microm in untreated samples to 2-10 microm in samples treated with Na2CO3--a pore-size more favorable for penetration of sulfur into the particles. The change in pore-size facilitates reaction with lime grains throughout the whole particle without rapid plugging of pores, avoiding premature change from a fast chemical reaction to a slow solid-state diffusion controlled process, as seen for untreated samples. Calcination in a thermogravimetric reactor showed that Na2CO3 increased the rate of calcination of CaCO3 to CaO, an effect which was slightly larger at 825 degrees C than at 900 degrees C. Peak broadening analysis of powder X-ray diffraction data of the raw, calcined, and sulfated samples revealed an unaffected calcite size (approximately 125-170 nm) but a significant increase in the crystallite size for lime (approximately 60-90 nm to approximately 250-300 nm) and less for anhydrite (approximately 125-150 nm to approximately 225-250 nm). The increase in the crystallite and pore-size of the treated limestones is attributed to an increase in ionic mobility in the crystal lattice due to formation of vacancies in the crystals when Ca is partly replaced by Na.
长期以来，人们已经知道某些添加剂（如氯化钠、氯化钙、碳酸钠、氧化铁）可以提高石灰石对二氧化硫的捕集能力。在最近的一项研究中，我们证明了极少量的碳酸钠对于生产具有非常高吸附能力的吸附剂非常有益。本文探讨了导致这些显著提高的因素。煅烧石灰石样品的压汞法测量结果表明，未处理样品的孔径从0.04 - 0.2微米变为用碳酸钠处理后样品的2 - 10微米，这种孔径更有利于硫渗透到颗粒中。孔径的变化有利于整个颗粒与石灰颗粒发生反应，而不会使孔隙迅速堵塞，避免了像未处理样品那样过早地从快速化学反应转变为缓慢的固态扩散控制过程。在热重反应器中进行的煅烧实验表明，碳酸钠提高了碳酸钙煅烧为氧化钙的速率，在825℃时的这种效果略大于在900℃时的效果。对原始、煅烧和硫酸化样品的粉末X射线衍射数据进行的峰展宽分析表明，方解石尺寸（约125 - 170纳米）未受影响，但石灰的微晶尺寸显著增加（从约60 - 90纳米增加到约250 - 300纳米），硬石膏的微晶尺寸增加较少（从约125 - 150纳米增加到约225 - 250纳米）。处理后石灰石微晶尺寸和孔径的增加归因于当钙部分被钠取代时，晶体中形成空位，从而导致晶格中离子迁移率增加。
