Biochars reduce mine land soil bioavailable metals

Biochars are being proposed as an amendment to remediate mine land soils. Therefore, two different feedstocks (pine beetle-killed lodgepole pine [Pinus contorta] and tamarisk [Tamarix spp.]), within close proximity to mine land affected soils, were used to create biochars in order to determine if they have the potential to reduce metal bioaccessibility. Four different mine land soils, contaminated with various amounts of cadmium, copper, lead, and zinc, received increasing amounts of biochar (0, 5, 10, and 15% by weight). Soil pH and metal bioaccessibility were determined, and the European Community Bureau of Reference sequential extraction procedure was employed to identify pools responsible for potential shifts in bioaccessibility. Increasing biochar application rates caused increases in soil pH (initial: 3.97; final: 7.49) and 55 to 100% (no longer detectable) decreases in metal bioaccessibility. The sequential extraction procedure supported the association of cadmium with carbonates, copper and zinc with oxyhydroxides and carbonates, and lead with oxyhydroxides; these phases were likely responsible for the reduction in heavy metal bioaccessibility. This study proved that feedstocks local to abandoned mining operations could subsequently be used to create biochars and reduce heavy metal bioaccessibility in mine land soils

Biochars impact on soil moisture storage in an Ultisol and two Aridisols

Excessive copper concentrations in water systems can negatively impact biological systems. Because copper can form strong associations with organic functional groups, we examined the ability of biochar (a carbon-enriched organic bioenergy by-product) to sorb copper from solution. In a batch experiment, potassium hydroxide-steam activated pecan shell biochar was shaken for 24 hours in pH 6, 7, 8, or 9 buffered solutions containing various copper concentrations to identify effect of pH on biochar copper sorption. Afterwards, all biochar solids from the 24 hours shaking period were air-dried and then analyzed using X-ray absorption fine structure spectroscopy to determine solid-phase copper speciation. In a separate batch experiment, biochar was shaken for 30 days in pH 6 buffered solution containing increasing copper concentrations; the copper sorption maximum was calculated based on the exponential rise to a maximum equation. Biochar sorbed increasing amounts of copper as the solution pH decreased from 9 to 6. The X-ray absorption fine structure results revealed that copper was predominantly sorbed onto a biochar organic phase at pH 6 in a molecular structure similar to copper adsorbed on humic acid. The X-ray absorption fine structure spectra at pH 7, 8, and 9 suggested that copper was associated with the biochar as three phases: 1) a complex adsorbed on organic ligands similar to copper on humic acid; 2) carbonate phases similar to azurite; and 3) a copper oxide phase like tenorite. The exponential rise equation fit to the incubated samples predicted a copper sorption maximum of 42,300 mg/kg copper. The results showed that potassium hydroxide-steam activated pecan shell biochar could be utilized as a material for sorbing excess copper from water systems, potentially reducing the negative effects of copper in the environment

Biochars impact on soil moisture storage in an Ultisol and two Aridisols

Excessive copper concentrations in water systems can negatively impact biological systems. Because copper can form strong associations with organic functional groups, we examined the ability of biochar (a carbon-enriched organic bioenergy by-product) to sorb copper from solution. In a batch experiment, potassium hydroxide-steam activated pecan shell biochar was shaken for 24 hours in pH 6, 7, 8, or 9 buffered solutions containing various copper concentrations to identify effect of pH on biochar copper sorption. Afterwards, all biochar solids from the 24 hours shaking period were air-dried and then analyzed using X-ray absorption fine structure spectroscopy to determine solid-phase copper speciation. In a separate batch experiment, biochar was shaken for 30 days in pH 6 buffered solution containing increasing copper concentrations; the copper sorption maximum was calculated based on the exponential rise to a maximum equation. Biochar sorbed increasing amounts of copper as the solution pH decreased from 9 to 6. The X-ray absorption fine structure results revealed that copper was predominantly sorbed onto a biochar organic phase at pH 6 in a molecular structure similar to copper adsorbed on humic acid. The X-ray absorption fine structure spectra at pH 7, 8, and 9 suggested that copper was associated with the biochar as three phases: 1) a complex adsorbed on organic ligands similar to copper on humic acid; 2) carbonate phases similar to azurite; and 3) a copper oxide phase like tenorite. The exponential rise equation fit to the incubated samples predicted a copper sorption maximum of 42,300 mg/kg copper. The results showed that potassium hydroxide-steam activated pecan shell biochar could be utilized as a material for sorbing excess copper from water systems, potentially reducing the negative effects of copper in the environment

Labile lead in polluted soils measured by stable isotope dilution

It is well known that lead (Pb) is strongly immobilized in soil by adsorption or precipitation. However, the reversibility of these reactions is poorly documented. In this study, the isotopically exchangeable Pb concentration in soils (E-value) was measured using a stable isotope (²⁰⁸Pb). Soils were collected at three industrialized sites where historical Pb emissions have resulted in elevated Pb concentrations in the surrounding soil. Lead concentrations ranged from background values, in the control soils collected far from the emission source, to highly elevated concentrations (5460–14440 mg Pb kg⁻¹). The control soil of each site was amended in the laboratory with Pb(NO₃)₂ to the same total Pb concentrations as the field-contaminated soils. The %E values (E-value relative to total Pb content) were greater than 84% in the laboratory-amended soils, and ranged from 45% to 78% (mean 58%) in the field-contaminated soils. The relatively large labile fractions of Pb in the field-contaminated soils show that the majority of Pb is reversibly bound despite the fact that the binding strength is large. The Pb concentrations in soil solution were up to 3500-fold larger for the laboratory-amended soils than for field-contaminated soils at corresponding total Pb concentrations. These differences cannot be explained by differences in labile fractions of Pb but are attributed to the decrease in soil solution pH upon addition of Pb²⁺-salt.F. Degryse, N. Waegeneers & E. Smolder