Iron-modified biochar inhibiting Cd uptake in rice by Cd co-deposition with Fe oxides in the rice rhizosphere.

Fe-enriched biochar has proven to be effective in reducing Cd uptake in rice plants by enhancing iron plaque formation. However, the effect of Fe on biochar, especially the biochar with high S content, for Cd immobilization in rice rhizosphere was not fully understood. To obtain eco-friendly Fe-loaded biochar at a low cost, garlic straw, bean straw, and rape straw were chosen as the feedstocks for Fe-enhanced biochar production by co-pyrolysis with Fe2O3. The resulting biochars and Fe-loaded biochars were GBC, BBC, BRE, GBC-Fe, BBC-Fe, and BRE-Fe, respectively. XRD and FTIR analyses showed that Fe was successfully loaded onto the biochar. The pristine and Fe-containing biochars were applied at rates of 0% (BC0) and 0.1% in pot experiments. Results suggested that BBC-Fe caused the highest reduction in Cd content of rice grain, and the reductions were 67.9% and 31.4%, compared with BC0 and BBC, respectively. Compared to BBC, BBC-Fe effectively reduced Cd uptake in rice roots by 47.5%. The exchangeable and acid-soluble fraction of Cd (F1-Cd) in soil with BBC-Fe treatment was 37.6% and 63.7% lower than that of BC0 and BBC, respectively. Compared to BC0, soil pH was increased by 0.53 units with BBC-Fe treatment. BBC-Fe significantly increased Fe oxides (free Fe oxides, amorphous Fe oxides, and complex Fe oxides) content in the soil as well. DGT study demonstrated that BBC-Fe could enhance the mobility of sulfate in the rhizosphere, which might be beneficial for Cd fixation in the rhizosphere. Moreover, BBC-Fe increased the relative abundance of Bacteroidota, Firmicutes, and Clostridia, which might be beneficial for Cd immobilization in the rhizosphere. This work highlights the synergistic effect of loaded Fe and biochar on Cd immobilization by enhancing Cd deposited with Fe oxides.

Pig manure biochar for contaminated soil management: nutrient release, toxic metal immobilization, and Chinese cabbage cultivation.

Pig manure could be an effective fertilizer source for soil, but with high concentrations of xic elements. It has been shown that the pyrolysis method could largely reduce the environmental risk of pig manure. However, the comprehensive analysis of both toxic metals immobilization effect and environmental risk of pig manure biochar applied as a soil amendment is rarely addressed. To address the knowledge gap, this study was carried out with pig manure (PM) and pig manure biochar (PMB). The PM was pyrolyzed at 450 â„ƒ and 700 â„ƒ, the corresponding biochar was abbreviated as PMB450 and PMB700, respectively. The PM and PMB were applied in a pot experiment growing Chinese cabbage (Brassica rape L. ssp. Pekinensis) with clay-loam paddy soil. The application rates of PM were set at 0.5% (S), 2% (L), 4% (M) and 6% (H). With the equivalent mass principle, PMB450 and PMB700 were applied at 0.23% (S), 0.92% (L), 1.84% (M), 2.76% (H), and 0.192% (S), 0.7% (L), 1.4% (M), 2.1% (H), respectively. Parameters of Chinese cabbage biomass and quality, total and available concentrations of toxic metals in soil, and soil chemical properties were systemically measured. The main results of this study showed that compared with PM, PMB700 was more effective than PMB450, which induced the highest reductions of Cu, Zn, Pb, and Cd contents in cabbage by 62.6%, 73.0%, 43.9%, and 74.3%, respectively. Both PM and PMB increased the total contents of metals (Cu, Zn, Pb, and Cd) in soil, and PMB decreased the mobility of Cu, Zn, Pb, and Cd at high application rates (≥2%). Treatment with H-PMB700 reduced CaCl2 extractable Cu, Zn, Pb, and Cd by 70.0%, 71.6%, 23.3%, and 15.9%, respectively. For Cu, Zn, Pb, and Cd fractions with BCR extraction, PMB treatments, especially PMB700, were more effective than PM in decreasing the available fractions (F1 +F2 +F3) at high application rates (≥2%). Overall, pyrolysis with high temperature (e.g., 700 â„ƒ) could significantly stabilize the toxic elements in PM and enhance PM's effect on toxic metals immobilization. The marked effects of PMB700 on toxic metal immobilization and cabbage quality improvement might be attributed to high ash contents and liming effect.

Effects of iron-modified biochar with S-rich and Si-rich feedstocks on Cd immobilization in the soil-rice system.

Fe-modified biochar has been shown to have high sorption ability for cadmium (Cd), while Cd immobilization effects of Fe-modified biochars with Si-rich and S-rich feedstocks have been rarely addressed. To explore the effects of Fe-modified Si-rich and S-rich biochars on Cd translocation in the soil-rice system, a pot experiment was carried out with an acidic Cd-contaminated sandy loam paddy from central South China and a late season rice cultivate during July to November 2018. Rice straw and rice husk were chosen as Si-rich feedstocks, and rape straw was applied as S-rich feedstock, these feedstocks were further collected and pyrolyzed at 450 °C. Pristine and Fe-impregnated rice straw (BRS/BRS-Fe), rice husk (BRH/BRH-Fe) and rape straw (BRE/BRE-Fe) biochars were applied at 0 and 10 t/ha, respectively. The reductions in Cd concentrations in rice grains were 23.8%, 22.3% and 46.1% with treatments of BRE, BRS and BRH, respectively, compared to the control. Compared to other pristine biochars, BRH is more effective in Cd remediation in paddy soil. For Fe-modified biochars, BRE-Fe achieved the highest reductions in Cd concentrations in rice grains with 46.7% and 30.1%, compared with the control and BRE, respectively. BRE-Fe decreased Cd remobilization from leaves to grains. Only BRE-Fe enhanced the formation and Cd sorption capacity of iron plaque. BRS-Fe and BRH-Fe enhanced Fe content in rice plants, which might induce the reduction in iron plaque formation. Fe and S-contained complexes contents increased in the contaminated pristine biochar particles, but reduced in the contaminated BRE-Fe particles. Therefore, Fe modification could not enhance Cd immobilization effect of Si-rich biochar, while Fe modified S-rich biochar has promising potential for Cd remediation with enhancement in iron plaque formation and Cd fixation in rice leaves.

Investigating the cadmium adsorption capacities of crop straw biochars produced using various feedstocks and pyrolysis temperatures.

Cadmium pollution in the environment is ubiquitous and can be a serious health issue. Crop straw-based biochar is a promising adsorbent, yet few studies have systematically examined the effects of both feedstock and pyrolysis temperature on biochar efficacy for cadmium (Cd) sorption. Sorption-desorption experiments were conducted to explore the mechanisms of Cd sorption for biochars derived from wheat straw (WSB), rape straw (RASB), soybean straw (SSB), and peanut straw (PSB) feedstocks, which were produced by pyrolysis at 450 °C and 650 °C. For biochars pyrolyzed at 450 °C, the sorption capacities varied as PSB>SSB>RASB≈WSB, while the order changed as RASB≈WSB>PSB>SSB for 650 °C biochars. With the increase in pyrolysis temperature, for wheat straw biochar and rape straw biochars, Cd sorption capacities increased by 72% and 63%, while there were 61% and 63% decreases for peanut straw biochar and soybean straw biochar, respectively. Compared to the non-legume straw biochars (WSB and RASB), legume straw biochars (SSB and PSB) have higher sorption capacities for Cd. Peanut straw biochar (PSB) produced at 450 °C was found to be the most promising adsorbent for cadmium. Examination of the sorbed biochars using a range of analytical techniques indicated that 450 °C PSB immobilized cadmium by precipitation with non-electrostatic adsorption. The precipitation of Cd on 450 °C PSB was mainly induced by cation exchange between Cd with mineral cations, which caused Cd complexation with carboxyl functional groups.

Effect of amendment of biochar supplemented with Si on Cd mobility and rice uptake over three rice growing seasons in an acidic Cd-tainted paddy from central South China.

To examine the effect of rice straw biochar and the synergism with silicon on Cd immobilization, a Cd-contaminated acidic sandy loam paddy, polluted from emissions from industrial activity, was chosen in central South China. A field trial was conducted over three rice growing seasons during 2016-2017. Rice straw biochar (BR), produced by the pyrolysis of rice straw pellets at 450 °C, was amended at 10 t/ha (BR1), 20 t/ha (BR2), and supplemented with 0.75 t/ha sodium silicate (SS) at 10 t/ha, (BR1 + SS) and 20 t/ha (BR2 + SS), compared to the control without biochar and sodium silicate (BR0). BR supplemented with Si enhanced Cd soil immobilization and decreased Cd accumulation in rice plant within three rice seasons. Compared to BR0, BR + SS reduced Cd concentrations in grains by 19.5-73.7%, higher than that of 8.6-50.2% following BR. Cd bio-concentration factor of the root was reduced by an average of 54.6% from BR + SS and by 19.0% from BR, compared to BR0 in last two rice seasons. BR + SS significantly increased soil pH and available Si, and soil CaCl2-Cd was negatively related to soil available Si (p < 0.05). The synergistic effect of BR and Si induced liming effect and co-precipitation of Cd with Si compounds during the aging process of biochar. Thus, we suggest that an alkaline silicon supplementation is used as an amendment to BR, which could be used as a strategic approach for tackling Cd contamination in South China rice paddies.

Biochar effects on uptake of cadmium and lead by wheat in relation to annual precipitation: a 3-year field study.

Biochar has been widely studied for its ability to reduce plant uptake of heavy metals by lowering metal bioavailabilities through adsorption and pH-driven fixation reactions. However, the long-term effect of biochar on heavy metal bioavailabilities in alkaline soils under natural redox condition is rarely studied. Here, we report a study examining the effects of biochar on bioavailability and partitioning of cadmium (Cd) and lead (Pb) among different soil fractions over 3 years in a field study with wheat (Triticum aestivum L.). Plots were established on two similar soils having low and high levels of contamination, both of which were amended in the first year with wheat straw biochar at 0, 20, and 40 t ha-1. Precipitation patterns varied greatly over the study period, with 2014 having record drought, which was followed by 2 years having extreme flooding events. Results showed a significant increase in grain yield and reductions in Cd and Pb concentrations in wheat grain in the biochar-amended soils in 2014. In contrast, bioavailable (exchangeable) heavy metal concentrations and plant uptake of Cd and Pb were significantly higher in the subsequent very wet years in 2015 and 2016, where the effects of biochar were much more variable and had an overall lesser effect on reducing heavy metal uptake. The results suggest that fluctuations in soil pH and redox caused by periodic drought and flood cycles strongly drive metal cycling through mobilization and immobilization of metals associated with different mineral phases. Under these conditions, biochar may have reduced efficacy for reducing heavy metal uptake in wheat.