Table 2.

Representation of specific biochars used for remediation of different soil heavy metals

S. No.	Biochar parent material	Pyrolysis temperature (℃)	Residence time (hours)	Application rate (optimum)	Biochar attributes to soil properties	Soil heavy metal remediated	Reference papers
1	Coffee husk	500	3	15t/ha	Increased soil electrical conductivity, total nitrogen, organic carbon, exchangeable cations, available phosphorus	Lead	(Bayu et al. 2016)
2	Wheat straw	350–550	–	40t/ha	Increased soil organic carbon, cation exchange capacity pH; decreased chemical mobility of Cd and stabilized it	Cadmium	(Cui et al. 2011)
3	Rice straw	500	4	5% (w/w)	Increased soil organic carbon, the abundance of Fe reducing bacteria, enhanced Arsenic methylation and volatilization by bio stimulating microbes	Arsenic	(Chen et al. 2017)
4	Rice straw	700	2	3% (w/w)	Increased soil pH, microbial biomass, nutrients, immobilized Cd (precipitation with Fe and Mn oxides) onto biochar surface	Cadmium	(Bashir et al. 2018c)
5	Chicken manure	700	4	–	Increased soil pH (alkalinity), mineral content (rich in phosphorus), ion exchange reactions, complexation and precipitation of heavy metals	Cadmium	(Huang et al. 2018)
7	Rice bran	700	6	0.625 g/L	Increased organic and mineral components are leading to the complexation of heavy metal ions	Cadmium	(Yiliang and Chen 2014)
8	Sewage sludge	900	–	0.2% (w/v)	Increased Cd adsorption by ion exchange with alkaline earth cation (Ca); increased pH mediating precipitation of Cd forming insoluble cadmium compounds	Cadmium	(Chen et al. 2015)
9	Macadamia nutshell	465	–	5% (w/w)	Reduced Cd and Pb bioavailability; increased soil pH mediating metal precipitation with carbonates; improved microbial carbon use efficiency	Lead, Cadmium	(Yilu et al. 2018)