Global perspectives for biochar application in the remediation of heavy metal-contaminated soil: a bibliometric analysis over the past three decades.

Herein, 7,308 relevant documents on biochar application for the remediation of heavy metal (HM)-contaminated soil (BARHMCS) from 1991 to 2020 were extracted from the Web of Science Core Collection and subjected to bibliometric and knowledge mapping analyses to provide a global perspective. The results showed that (1) the number of publications increased over time and could be divided into two subperiods, i.e., the slow growth period (SGP) and rapid growth period (RGP), according to whether the annual publication number was ≥300. (2) A total of 126 countries, 741 institutions, and 1,021 scholars have contributed to this field. (3) These studies are mainly published in Science of the Total Environment, Chemosphere, etc., and are mainly based on the categories of environmental science, soil science, and environmental engineering. (4) The top five keyword clusters for the SGP were biochar, biochar, sorption, charcoal, and HMs, and those for the RGP were adsorption, black carbon, nitrous oxide, cadmium, and pyrolysis. (5) The main knowledge domains and the most cited references during the SGP and RGP were discussed. (6) Future directions are related to biochar application for plant remediation, the mitigation of climate change through increased carbon sequestration, biochar modification, and biochar for HMs and multiple organic pollutants. Biochar application in the remediation of heavy metal-contaminated soil (BARHMCS) has become a popular research topic worldwide. Many excellent papers on this topic have been published, including some valuable reviews. However, there are no reviews including bibliometric and visual analyses. In the present study, bibliometric and visual analyses of relevant literature in the field of BARHMCS based on the Web of Science Core Collection were carried out to outline the development process of this field at a macro level, clarify the research hotspots, identify the knowledge domains that support this field, and explore future research directions. These efforts will no doubt help readers fully understand BARHMCS from a global perspective and provide a reference for future research. An overall global perspective of biochar remediation of heavy metal (HM)-contaminated soil was provided. The main popular research topics of each period were discussed. Knowledge domains were discussed. Five main future research directions were identified based on burst keyword analysis. Biochar modification and its effect on HMs and coexisting organic pollutants should be studied in the future for soil remediation purposes. [ABSTRACT FROM AUTHOR]