Co-pyrolysis of corn stover with industrial coal ash for in situ efficient remediation of heavy metals in multi-polluted soil

Coal ash incorporated biochar (CA/BC) composite was prepared by co-pyrolysis of agricultural residue and in-dustrial coal ash and applied for remediation of soils polluted by lead (Pb) and cadmium (Cd). The results showed that immobilization efficiency of CA/BC for heavy metals (HMs) was significantly enhanced by 77.1 % (Pb) and 42.7 % (Cd) compared to pristine biochar (BC), and this was mainly due to the increased pH value, surface functionality and surface negative charge. By the introduction of 5 % CA/BC, the polluted soils showed the highest reduction of leaching toxicity by 67.9 % (Pb) and 49.7 % (Cd), respectively. The chemical speciation of Pb and Cd in soils was changed remarkably and the reduced bioavailable Pb and Cd were mainly transformed from acid-soluble fraction into the most stable form of residual fraction. The mechanism study showed that surface precipitation, complexation, cation exchange and cation-pi interaction of CA/BC mainly contributed to heavy metals (HMs) immobilization. The pot experiments further confirmed that incorporation of 5 % CA/BC effectively reduced plant Pb and Cd accumulation by 81 % and 62.5 % respectively, and significantly promoted the plant growth of paddy rice by 3.1, 2.2 and 2.0 times in terms of root, stem length and dry mass parameters. The present study offered a cost-effective and green method to prepare soil amendment with great potential for remediation of soils polluted by HMs and realized the value-added utilization of waste agricultural residue and industrial coal ash.

Automated summary

The immobilization efficiency of CA/BC for heavy metals was significantly enhanced due to increased pH value, surface functionality, and surface negative charge. The introduction of 5% CA/BC led to the highest reduction of leaching toxicity in polluted soils. The chemical speciation of Pb and Cd in soils changed remarkably, with bioavailable Pb and Cd mainly transformed into the most stable form of residual fraction.