Adsorption and desorption of Cu(II) and Pb(II) in paddy soils cultivated for various years in the subtropical China

Copper and zinc adsorption by softwood and hardwood biochars under elevated sulphate-induced salinity and acidic pH conditions

“…As a result, the proportion of Cu hydroxides under the final pH conditions would be much higher than that of Zn hydroxides in the solution. The carbon surface of biochars and activated carbon had a higher adsorption affinity for species of metal hydroxides than free ions of metals (Ma et al, 2010;Tong et al, 2011;Jiang et al, 2012). Therefore, the magnitude of increase in Cu adsorption with rising pH by both biochars and activated carbon was larger than the Zn adsorption (Fig.…”

“…Mechanisms involved in heavy metal retention by biochars mainly involve: (i) the formation of metal hydroxide, carbonate, or phosphate precipitates (Uchimiya et al, 2010); (ii) ion exchange, which leads to the release of H + and other metal ions (e.g., Ca 2+ , Mg 2+ , Na + and K + ) (Mohan et al, 2007); and (iii) complexation with functional groups such as carboxyl or hydroxyl groups (Jochová et al, 2004;Ahmad et al, 2014a). The adsorption of heavy metals in the biochars is influenced by solution pH and electrolyte composition (Rivera-Utrilla and Sánchez-Polo, 2011) (Ma et al, 2010;Tong et al, 2011;Jiang et al, 2012). A range of pH conditions from acidic to alkaline pH may be expected in base metal mine tailings, depending on the acid generation and neutralizing capacity of tailings minerals concerned (such as pyrite, and calcite) (Dold and Fontboté, 2002).…”

Amendment of biochar reduces the release of toxic elements under dynamic redox conditions in a contaminated floodplain soil

“…In addition, the higher pH in CS + BC compared to CS might have enhanced the hydrolysis of Cu 2+ to form Cu(OH) + , Cu(OH) 2 , or even precipitation of Cu as hydroxides (Cu 2+ + 2OH À = Cu(OH) 2 ) (Stumm and Morgan, 1996). With an increase in pH, more Cu 2+ was likely sorbed by variable-charge soil components, which have a higher sorption affinity for Cu-OH than Cu 2+ (Ma et al, 2010).…”

Immobilization of Cu(II), Pb(II) and Cd(II) by the addition of rice straw derived biochar to a simulated polluted Ultisol

“…The portion of oxidizable Cu(II) was much higher than that of Pb(II) under the same conditions. This was primarily attributed to the high affinity of organic functional groups on the biochar for Cu(II) [36,37].…”

“…Consequently, the affinity of the biochar amended soil surface for cations likely increased. In addition, increased pH led to increased hydrolysis of heavy metals, which also increased the specific adsorption of heavy metals by the variable charge soils because the soil surface has a higher adsorption affinity for species of metal hydroxides than free ions of heavy metals [37].…”