Combined application of strong alkaline materials and specific organic fertilizer accelerates nitrification process of a rare earth mining soil

Min Wang; Song Wu; Yilin Lu; Haotian Wu; Dunfeng Si; Dongmei Zhou

doi:10.1016/j.scitotenv.2023.163042

Combined application of strong alkaline materials and specific organic fertilizer accelerates nitrification process of a rare earth mining soil

Sci Total Environ. 2023 Jun 25:879:163042. doi: 10.1016/j.scitotenv.2023.163042. Epub 2023 Mar 23.

Authors

Min Wang¹, Song Wu², Yilin Lu¹, Haotian Wu¹, Dunfeng Si¹, Dongmei Zhou³

Affiliations

¹ State Key Laboratory of Pollution Control & Resources Reuse, School of the Environment, Nanjing University, Nanjing 210023, China.
² State Key Laboratory of Pollution Control & Resources Reuse, School of the Environment, Nanjing University, Nanjing 210023, China. Electronic address: songwu@nju.edu.cn.
³ State Key Laboratory of Pollution Control & Resources Reuse, School of the Environment, Nanjing University, Nanjing 210023, China. Electronic address: dmzhou@nju.edu.cn.

PMID: 36965722
DOI: 10.1016/j.scitotenv.2023.163042

Abstract

The extensive usage of ammonium sulfate as the leaching agent to extract rare earth elements led to widespread ammonia nitrogen (NH₄⁺-N) pollution in the tailing soils of ion-adsorbed rare earth deposits in southern China. However, the cost-effective technologies to tackle with the long-term retention of NH₄⁺-N in the rare earth mining soil have been largely unresolved. In this study, we developed a cost-effective approach to activate soil nitrification by the co-application of alkaline materials and organic fertilizer. The co-application of 0.3 % of organic fertilizer and 0.1 % ∼ 0.2 % of CaO or MgO or Mg(OH)₂ stimulated a soil NH₄⁺-N decrease rate of 2.01-7.58 mg kg^-1 d^-1 and a soil NO₃^--N accumulation rate of 1.56-7.09 mg kg^-1 d^-1. Noting that only if the soil pH was elevated to 7.81-9.00, the NH₄⁺-N decrease rate and NO₃^--N accumulation rate were dependent on the proton consumption capacity of the alkaline materials. The application of CaCO₃ could not stimulate soil nitrification possibly due to the soil pH was uncapable to be elevated to above 7.68. The qPCR, amplicon sequencing, and nitrification inhibitor batch incubation results demonstrated that organic fertilizer supplied active ammonia-oxidizing bacteria Nitrosomonas europaea. The proliferation of Nitrosomonas europaea in the alkaline materials and organic fertilizer co-applied soil was responsible for the soil nitrification. Furthermore, the application of commercial denitrifying bacteria inoculum promoted the removal of accumulated NO₃^--N. The findings of this study provide a lost-cost technology to remove NH₄⁺-N from the rare earth mining soil.

Keywords: Alkaline materials; Ammonia nitrogen; Ammonia-oxidizing bacteria; Nitrification; Rare earth mining.