Biochar from pyrolysis of deinking paper sludge and its use in the treatment of a nickel polluted soil

•Biochar from de-inking paper sludge can be used to reclamation of soils polluted by Ni.•Addition of biochar reduced the mobility, bioavailability and leaching of and Ni.•Addition of biochar reduced soil CO2 emissions.

An increasing proportion of recycled fibers are used in paper industries due to their important environmental and economic benefits. However, removing the ink, clay, coatings and contaminants from paper waste in order to produce recycled fibers creates large amounts of de-inking paper sludge. For this reason, the preparation of biochar from pyrolysis process of this kind of waste rich in cellulose fibers, carbonates and clays, and their use in soil remediation contaminated by heavy metals can be perceived as an interesting valorization alternative. The aim of the present work is to study the influence of biochar from de-inking paper sludge (HP) pyrolysis in a Ni2+ polluted soil. Selected soil (S) was artificially contaminated with Ni2+ at 1000 mg Ni kg−1 (S1000) and then amended at a rate of 5 wt% using HP and two biochars prepared from pyrolysis of HP at 300 °C (HP300) and 500 °C (HP500). Non-contaminated soil (S) was used as control and amended with the same rate of HP, HP300 and HP500. An incubation experiment was designed and soil CO2 emissions were measured in the different treatments during 77 days. The results have shown that CO2 emissions followed the order S = S + HP = S + HP300 > S + HP500 for the non-polluted soil and the patternS1000 + HP300 > S1000 ≈ S1000 + HP > S1000 + HP500 for the soil spiked with Ni. Finally, it was observed that HP500 addition to the polluted soil reduced the quantity of mobile, leached and bioavailable Ni.