Remediation of Soil Polluted with Cd in a Postmining Area Using Thiourea-Modified Biochar

Abstract

Cadmium presence in soil is considered a significant threat to human health. Biochar is recognized as an effective method to immobilize Cd ions in different soils. However, obtaining effective and viable biochar to remove elevated Cd from postmining soil remains a challenge. More modifiers need to be explored to improve biochar remediation capacity. In this investigation, pot experiments were conducted to study the effects of poplar-bark biochar (PBC600) and thiourea-modified poplar-bark biochar (TPBC600) on Cd speciation and availability, as well as on soil properties. Our results showed that the addition of biochar had a significant influence on soil properties. In the presence of TPBC600, the acid-soluble and reducible Cd fractions were transformed into oxidizable and residual Cd fractions. This process effectively reduced Cd bioavailability in the soil system. Compared to PBC600, TPBC600 was more effective in improving soil pH, electrical conductivity (EC), organic matter (SOM), total nitrogen (TN), ammonium nitrogen (NH4+-N), nitrate nitrogen (NO3--N), available potassium (AK), available phosphorus (AP), and available sulfur (AS). However, this improvement diminished as incubation time increased. Results of Pearson correlation analysis, multivariate linear regression analysis, and principal component analysis showed that soil pH and available phosphorus played key roles in reducing the available cadmium in soil. Therefore, TPBC600 was shown to be an effective modifier that could be used in the remediation of soil polluted with Cd.

Preliminary Findings on Cadmium Bioaccumulation and Photosynthesis in Rice (Oryza sativa L.) and Maize (Zea mays L.) Using Biochar Made from C3- and C4-Originated Straw

“…Cd–biochar treatments significantly increased pH compared to the control. These results are in line with some previous studies which reported that using CaO-containing biochar in Cd-polluted treatment caused an increase in soil pH due to dissolving CaO and release of OH-ions into the soil solution [ 16 , 20 ]. In addition, the availability of N, P, and K also sharply increased in BC3 and BC4 treatments.…”

“…Moreover, the accessibility of nitrates, phosphate potash, and sulfates in soil, which do not have the same chemical characteristics as Cd, is prevented by the Cd bioaccumulation. A decrease in macronutrients in the tissue due to high concentrations of Cd has been reported in previous pieces of literature [ 16 , 20 ].…”

“…As the research site is located in a tropical region and thereby generally influenced by high precipitation and temperature, it is exposed to the loss of basic cations [ 19 ]. Biochars produced from crop residues are here able to prevent re-acidification of acidic soils by boosting the soil pH-buffering capacity [ 20 ]. Large surface area of biochar with considerable functional groups (for example, carboxylic and phenolic groups) is the key factor to increasing the pH of biochar [ 5 ].…”

Biochar rebuilds the network complexity of rare and abundant microbial taxa in reclaimed soil of mining areas to cooperatively avert cadmium stress

“…About 2.5 kg of soil was thoroughly mixed with biochar at a ratio of 2% (w/w) and filled into a polyethylene flowerpot with a height of 12 cm and a diameter of 13 cm. Our previous study confirmed that the best Cd stabilization effect was obtained at this biochar ratio ( Zhu et al, 2020b ). The treatment group without biochar was the control (CK) group, and the treatment group with poplar bark biochar and thiourea-modified biochar were the PB and TP treatment groups, respectively.…”

Effects of biochar on the transformation of cadmium fractions in alkaline soil

“…Regardless of the Cd 2+ presence in water or in soil, biochar has high adsorption capacity through functional groups, physical adsorption, and electrostatic attraction, with the biochar modification also having extensive research prospects [ [8] , [9] , [10] , [11] ]. As a good adsorbent and soil conditioner, biochar can not only directly adsorb and bind heavy metals through surface functional groups [ 12 , 13 ], but also affect Cd fractions by changing both the soil physicochemical properties and microbial community structure [ [14] , [15] , [16] ]. For example, [ 17 ] showed that coconut shell biochar significantly reduced the available Cd content in soil, improved soil urease activity, and increased the relative abundance of soil microbial community.…”