煅烧对白云石治酸效果及其钙镁释放动力学特性的影响

针对中国土壤普遍酸化,而用石灰治理会导致土壤板结,用碱性工业废弃物治理又有二次污染风险等问题,该研究在低温煅烧工艺下,研究了白云石颗粒大小、煅烧时间对白云石碱度、微结构、钙镁释放动力学特征的影响,旨在为开发既能治酸改土又能供应钙镁养分的白云石煅烧工艺提供理论依据。研究提出了总碱度和短期累积碱度2个概念。结果表明:粒径从0.15到3 mm的白云石,经过1 h煅烧后,总碱度增加了78%、短期累积碱度提高了1 100倍。粒径为1～3 mm的煅烧白云石在煅烧1～3 h后钙镁的释放速率快慢的规律一致,以煅烧2 h后释放速率最快。钙、镁释放曲线可用Parabolic、一级动力学、Richards和Bertallanffy方程进行拟合。其中Bertallanffy修正方程最适于描述煅烧白云石CaO释放的规律;Richards和Bertallanffy修正方程适于定量描述MgO的释放规律。由此可见,白云石煅烧后具有较高治酸潜力(总碱度)又有较大的治酸强度(短期累积碱度),并且能促进钙镁的释放,钙镁供肥量可用Richards和Bertallanffy修正方程预测预报。就粒径1～3 mm的白云石而言,煅烧1 h是增加其总碱度的经济煅烧时间,但是促进其快速裂解、提高其治酸强度和钙镁有效性的最佳煅烧工艺是850℃和2 h。

Effects of calcinated dolomite on the amendment of acid soil and release kinetics of Ca-Mg

Abstract: Widespread soil acidification in China has posed a series of severe problems on agriculture ecosystems. In previous control measures, the use of lime can lead to soil hardening, whereas, industrial alkaline wastes inevitably face the risk of secondary pollution. Recently, cheap dolomite can be expected to serve as a soil functional conditioner, particularly for providing adequate amounts of calcium and magnesium nutrients for crops. This paper aims to investigate the effects of particle size and calcination time on dolomite alkalinity, microstructure, and release kinetic characteristics of calcium and magnesium during a low temperature calcination process. Two concepts were proposed, the capacity of alkalinity and short-term cumulative alkalinity, in order to evaluate the acid treatment of calcined dolomite. The results showed that after the calcination of dolomite with a particle size less than 3mm, the capacity of alkalinity increased by 78%, and the short-term cumulative alkalinity increased by 1,100 times, whereas the calcination time was extended from 1 hour to 3 hours without significantly increasing the total alkalinity. After calcining dolomite with a particle size of 0.15 to 0.25 mm, the release rate of calcium and magnesium reached the maximum after 3-hour calcination. However, the calcined dolomite with a particle size of 1 to 3 mm indicated a stable release rate of calcium and magnesium after the calcination for 1 to 3 hours, and the maximum release rate occurred after the calcination for 2 h. After 26-day incubation, the cumulative release rate of calcium in the calcined dolomite was over 87%, and the cumulative release rate of magnesium was less than 9%. Release curves of calcium and magnesium from calcined dolomite can be fitted using parabolic, first order kinetics, Richards and Bertallanffy equations. The modified Bertallanffy equation can be the most suitable to describe the release change of CaO amount from calcined dolomite over time, where r = 0.990-0.999, SE=0.47-1.53. Richards and the modified Bertallanffy equations can be used to quantitatively describe the MgO release pattern of dolomite, or predict the amount of magnesium supplied by dolomite. The goodness of fit test of the Richards equation was r=0.959-0.985, SE=0.14-0.20, while that of the modified Bertallanffy equation was r=0.980-0.993, SE=0.13-0.19. It infers that the calcined dolomite can serve as high capacity and intensity of alkaline, total and short-term cumulative alkalinity, while the calcination process can promote the release or supply of calcium and magnesium, where the release rate can be predicted by using Richards and modified Bertallanffy equations. In the calcinated dolomite with a large particle size of 1 to 3 mm, 1 hour can be an economical calcination time to increase its capacity of alkalinity, whereas the optimum is 2 hours calcination process to promote rapid cracking, short-term cumulative alkalinity, effective calcium and magnesium. The research results can provide a theoretical basis for calcinated dolomite translating to serve as soil conditioner and its manufacturing process.