不同pH条件下生物质灰渣中K^+释放动力学研究

Analysis of K^+ release kinetics of biomass ash with different pH

试验选取4种生物质灰渣(玉米灰渣、水稻灰渣、锯木灰渣和谷壳灰渣)为研究材料,以不同pH(4、7、9)的NH4Ac为交换液,采用渗透交换法,研究了生物质灰渣中K+的释放动力学特征。结果表明,在pH为4、7和9条件下,供试生物质灰渣中K+释放量在20~80 min达到平衡,平衡释放量分别为14.77~255.17 cmol·kg-1、4.83~106.71 cmol·kg-1和12.11~224.33 cmol·kg-1。相关分析表明,K+释放量与生物质灰渣中全钾含量极显著相关,说明受生物质灰渣中全钾含量影响,其K+释放平衡时间和释放量存在显著差异。方差分析显示,同一生物质灰渣中K+释放速率在不同pH条件之间存在极显著差异。由此可见,受交换液pH和全钾含量的影响,不同生物质灰渣中K+的释放量和平衡时间均存在较大差异。不同pH条件下,水稻灰渣和玉米灰渣K+释放量(Q)表现为Q4>Q9>Q7,锯木灰渣和谷壳灰渣的释放量表现为Q9>Q4>Q7;在3种pH条件下,4种生物质灰渣K+的释放总量均表现为Q水稻灰渣>Q锯木灰渣>Q谷壳灰渣>Q玉米灰渣。平衡前不同时段K+的释放率(v)与反应时间的自然对数(lnt)极显著相关。4种生物质灰渣K+的释放动力学最适模型均表现为:pH=4时为Elovich方程,pH=7时为双常数方程,pH=9时为Elovich方程;同一pH条件下,4种生物质灰渣的模型拟合性最优为Elovich方程,双常数方程次之,抛物线扩散方程最差。

Biomass ash is a kind of plant straw residuum produced by combustion of straw at 800 ℃. Biomass ash contains lots of nutrients, including phosphorus （P）, calcium （Ca）, magnesium （Mg） and especially potassium （K）. In biomass ash, K mainly occurs as K2SO4, KCl and K2SO3. In recent years, biomass ash has been used to produce potassium-based fertilizers. However, less work has been done on the principles and mechanisms of biomass ash K＋ release. In the new production system and method proposed to produce potassium fertilizers from biomass ash, pH is critical for K＋ release. This paper used four types of biomass ash （cornstalk, rice straw, sawn wood and chaff） with different pH of 4, 7 and 9 adjusted by ammonium acetate （NH4Ac） to extract available K by the method of penetration exchange. This study discussed the cumulative quantity and rate of release of K＋, and analyzed K＋ release dynamics of four types of biomass ash using three kinetic models. The results indicated that K＋ release attained equilibrium in 20 80 min with a total capacity of K＋ release significantly different for different pH. Total K＋ release capacity was 14.77 255.17 cmol·kg-1 at pH of 4, 4.83 106.71 cmol·kg-1 at pH of 7 and 12.11 224.33 cmol·kg-1 at pH of 9. Total K＋ release capacity under each pH condition showed that rice straw released the most K＋, followed by cornstalk and sawn wood, while chaff released the least K＋. Correlation analysis suggested that total K content of biomass ash was critical for the time and total capacity of K＋ release. The correlation coefficient of released K＋ amount and total K content was 0.991 0.997. A significant difference was noted in K＋ release rate among biomass ash types. These implied that the greater content of K contain the more amount of K＋ release. This indicated that equilibrium time and quantity of released K＋ varied with pH and total K content of exchange solution. Under the three pH conditions, released K＋ amounts （Q） of rice straw and cornstalk were in the order of Q4 〉 Q9 〉 Q7, while those of sawn wood and chaff were Q9 〉 Q4 〉 Q7. The order of total K＋ release capacity of biomass ash was QRice straw 〉 QSawn wood 〉 QChaff 〉 QCornstalks under the three pH conditions. Before equilibrium time, K＋ release velocity （v） was logarithmically related with time （lnt） during each reaction stage. For the same biomass ash, the optimal kinetic mode of K＋ release changed with pH condition. The best models at pH of 4, 7 and 9 were Elovich Equation （EE）, Dual Constant Equation （DCE） and EE, respectively. Under the same pH condition, the model that best described K＋ release process was the EE and DCE, while the Parabolic Diffusion （PD） was the most inappropriate model.