Table 7.
Summary of various engineered/modified biochars and their immobilization efficiency for metals/metalloids in the soil system.
| Biochar type | Pyrolysis temperature (°C) | Modification technique | Metalloids | Application rate/dose | Findings | References |
|---|---|---|---|---|---|---|
| Carrot pulp | 550 | Thiol-modification | Zinc (112 mg kg−1), Copper (29 mg kg−1) | 4 and 8% | As compared to pristine biochar, thiourea-doped-biochar was more efficient in converting labile fractions to stable fractions of Zn/Cu in soil | 149 |
| Corncob | 600 | Magnesium chloride hexahydrate | Lead (3410 mg kg−1) | 5% | MgO-coated biochar addition induced a significant 50% reduction in TCLP-leached Pb2+ in soil-washing residue | 150 |
| Peanut shell | 600 | CTAB | Chromium (1992 mg kg−1) | 1,2 and 5% | Engineered-biochar exhibited higher Cr(VI) immobilization in soil, as showed by the substantial reductions in the bio-accessibility, (up to 97%), leachability (100%), and bioavailability (up to 92%) of Cr6+ than the pristine biochar | 151 |
| Rice straw | 600 | Red mud | Arsenic (122 mg kg−1) | 1% | Modified biochar reduced (27%) of the Sodium bicarbonate-extractable arsenic, which is more efficient than using red mud (6%) and biochar (23%) alone | 27 |
| Wheat straw | 500 | Goethite | Arsenic (10 mg kg−1), Cadmium (10 mg kg−1) | 2% | The arsenic and Cadmium content of Oryza sativa grains were reduced by 77% and 85%, respectively | 34 |
| Tea branch | 500 | Manganese ferrite | Cadmium (696 mg kg−1), Antimony (79 mg kg−1) | 0.1, 1 and 2% | Ammonium nitrate -the extractable amount of antimony in soil reduced by 33 to 43% with Manganese ferrite-doped biochar treatments; the maximum reduction of Calcium chloride-extractable cadmium (up to 76%) was found at 2% additional dose | 62 |
| Rice straw | 500 | Thiol-modification | Lead (1182 mg kg−1), Cadmium (9.2 mg kg−1) | 1 and 3% | Thiol-doped biochar decreased the soil-available lead by 8 to 11% and soil-available cadmium by 34 to 39% | 7 |
| Coconut shell | 800 | HCl and Ultrasonication |
Cadmium (0.82 mg kg−1), Nickel (66 mg kg−1) Zinc (184 mg kg−1) |
2.5 and 5% | 5% engineered biochar addition resulted in soil-available zinc, nickel, and cadmium reduced by 30%, 57%, and 12%, respectively | 32 |
| Maize stalk | 500 | Polyethyleneimine | Cadmium (0.4 mg kg−1) | 2600, 5200, and 13,000 kg ha−1 | Polyethyleneimine-treated biochar decreased the cadmium uptake in the wheat by 40 to 80%; soil physicochemical characteristics such as CEC, pH, enzyme activities, and soil aggregates stability were increased after the application of polyethyleneimine-loaded | 152 |
| Maize stalk | 350 | Immobilization with Citrobacte, Bacillus cereus and Bacillus subtilis sp. |
Uranium (29 mg kg−1) Cadmium (2 mg kg−1) |
3% | The diethylenetriaminepentaacetic acid -extractable cadmium and cadmium in the soil reduced by 56 and 69%, respectively; bacteria-modified biochar decreased metal uptake hence stimulating celery growth | 84 |
| Fabric waste | 600 | Chitosan | Cadmium (20 mg kg−1) | 5% | Chitosan-doped biochar application reduced the distribution of cadmium in roots (up to 54%), shoots (upto73%), and soil available cadmium (up to 58%) relative to control | 153 |
| Wheat straw | 500 | Bismuth nitrate pentahydrate | Arsenic (47 mg kg−1) | 1,2 and 5% | The Bismuth nitrate pentahydrate-modified biochar reduced the (non)specifically adsorbed arsenic as the application rate raised, whereas pristine biochar caused the arsenic release | 154 |
| Animal manure | 450 | nZVI and chitosan | Chromium (100 mg kg−1) | 5% | The engineered biochar exhibited simultaneous sorption of Cr3+ via precipitation and surface complexation and reduction of Cr6+ to Cr3+ | 57 |
| Rice husk | 550 | Sulfur | Mercury (1000 mg kg−1) | 5% | Compared to the control, 5% Sulfur-loaded biochar decreased freely available mercury in TCLP leachates by 99% | 38 |
| Corn straw | 400 | Immobilization with Pseudomonas | Copper (247 mg kg−1), Cadmium (56 mg kg−1) | 5% | The addition of bacterial-modified biochar decreased the diethylenetriaminepentaacetic acid -extractable cadmium/copper | 19 |
| Corn straw | 700 | Ball milling | Lead (33 mg kg−1), Cadmium (1.28 mg kg−1) | 2% | Soil-available lead and cadmium were reduced by 34% and 48%, respectively; Lead and cadmium uptake by corn was reduced | 30 |
| Brassica napus | 600 | Ultraviolet radiation | Cadmium (1.9 mg kg−1) | 0.2,0.4 and 0.6% | With engineered biochar treatments, the Calcium chloride-extractable cadmium was decreased by 18 to 51%; and the uptake of cadmium in plant shoots was reduced by 67 to 82% | 32 |
| Bamboo | 700 | Al/Mg LDH | Uranium (33 mg kg−1) | 10% | Modified biochar application decreased the cumulative loss (up to 53%) and leaching efficacy (54%) of uranium, relative to control | 32 |
| Kenaf bar | 600 | Ferrous sulfate heptahydrate | Cadmium (10 mg kg−1) | 5% | Residual fractions of cadmium enhanced by 45% due to the Cd(II) complexation with iron hydroxides | 34 |
| Plant residues | 650 |
Lead (736 mg kg−1) Cadmium (0.5 mg kg−1), Arsenic (141 mg kg−1) |
Ferric chloride hexahydrate | 3% | Fe-loaded biochar was suggested for remediation of Arsenic-polluted paddy soils while fresh biochar might be more appropriate for cadmium and lead remediation; bioavailability of lead, cadmium, and arsenic reacted differently to different water management regimes | 39 |