过磷酸钙对氨气的吸附解吸特性研究

Adsorption and desorption of calcium superphosphate to ammonia gas

禽畜粪便堆肥过程中氨气挥发既导致肥料养分下降又使周边环境出现恶臭,常用的化学磷肥过磷酸钙,由于其含有的游离酸可与氨反应,是潜在的堆肥挥发氨气回收固定的吸附剂.本研究以氨水挥发出来的氨气来模拟堆肥过程中的氨挥发,以过磷酸钙含氮量表征其对氨的吸附,分析过磷酸钙对氨气的吸附解吸特性及其pH的变化.结果表明:过磷酸钙对氨气吸附达到饱和后,含氮量可达干重的12%左右,pH升高到11.5,呈现较强的碱性;氨吸附饱和过磷酸钙在不同方式放置时,会逐渐解吸,pH也会随之下降,其中在空气中自然放置时,吸附氨氮含量最终降低到4%左右,pH值为6.21;密封保存时降低到6%左右,pH值为7.54;与氨同时挥发的水蒸汽也可被过磷酸钙大量吸附,并对氨的吸附具有影响.过磷酸钙吸附氨饱和后呈强碱性,施用土壤不利于作物吸收,且在保存过程中会再次损失氨,实际应用时应避免;而使吸附氨氮含量维持在4%～6%,pH则处于较易被植物吸收利用的中性范围,固定的氨也比较稳定.

Ammonia emission in poultry manure composting not only results in nitrogen loss,but also acts as the source of odor.Calcium Superphosphate （CSP） is a typical chemical fertilizer containing free acid which could bond ammonia by chemical reaction.Therefore,CSP can be used as a potential sorbent of ammonia gas from composting,which will form compound fertilizer of phosphorus and nitrogen.This study was conducted to investigate the adsorption and desorption characteristics of CSP to ammonia gas.The aqua ammonia was selected as a source of ammonia gas.Both the nitrogen content in CSP which reflected the ammonia absorbed and pH were monitored.The nitrogen content reached about 12% of CSP （dry weight） when the adsorption was saturated.Concurrently,its pH increased largely and reached 11.5.When the CSP with ammonia saturation was stored in different ways,the nitrogen content reduced gradually due to desorption of ammonia partly,and its pH decreased correspondingly.Ultimately,the nitrogen content reduced to about 4% when the CSP was exposed in the air,and to about 6% when the CSP was put into sealed bag without complete air evacuation.The pH of CSP ranged from 6.21 to 7.54 after ammonia desorption in both aforementioned disposal ways.Water vapour evaporated from aqua ammonia was also adsorbed by CSP largely,which affected the ammonia adsorption.The CSP with ammonia saturation had too high pH to be used directly as a fertilizer of crop.Moreover,it also lost some ammonia due to high pH when stored.Therefore,the adsorption saturation should be avoided when the CSP was used as a sorbent of ammonia gas from composting.For CSP adsorbing ammonia,it was suitable to be a fertilizer that the nitrogen content kept at 4%～6% with pH near to 7.