Nickel Hyperaccumulator Biochar as a Ni-Adsorbent and Enhanced Bio-ore

Abstract

Increasing nickel (Ni) demand may spur the need for creative Ni production methods. Agromining (farming for metals) uses plants that can accumulate high concentrations of metal in their biomass, called bio-ore, as a metal extraction strategy. Furthermore, biochar, produced by biomass pyrolysis under low-oxygen conditions, can be used to remove Ni from contaminated wastewaters. In this work we investigate whether biochar synthesized from the Ni-hyperaccumulating plant Odontarrhena chalcidica (synonymous Alyssum murale ) can be used as a Ni-adsorbing biochar. We grew O. chalcidica on soils with varying Ni concentration, characterized the plants and resultant biochars synthesized at different pyrolysis temperatures, and analyzed Ni batch adsorption results to determine the adsorption capacity of O. chalcidica biochar. We found that Ni concentration in O. chalcidica increases with increasing soil Ni but reaches an accumulation limit around 23 g Ni kg –1 dry weight in dried leaf samples. Pyrolysis concentrated Ni in the biochar; higher pyrolysis temperatures led to higher biochar Ni concentrations (max. 87 g Ni kg –1 ) and surface areas (max. 103 m 2 /g). Finally, the O. chalcidica biochar adsorption results were comparable to high-performing Ni adsorbents in the literature. The adsorption process greatly increased the Ni concentration in some biochars, indicating that synthesizing biochar from O. chalcidica biomass and using it as a Ni adsorbent can produce a Ni-enhanced bio-ore with nickel content higher than all nickel-rich veins currently mined.

Nickel Hyperaccumulator Biochar Sorbs Ni(II) from Water and Wastewater to Create an Enhanced Bio-ore

“…Both showed high pH and acid neutralizing capacity relative to other biochars in the literature; the accumulated Ca as CaCO 3 in the leaf trichomes and K throughout the plants likely contributed to these characteristics. , High pH and acid neutralizing capacity can enhance Ni­(II) sorption from solutions with extremely acidic initial pH, since Ni­(II) sorption primarily occurs above pH 5 . C900 had a slightly higher surface area than MN900, though both were similar and of the magnitude expected from previous results . The N 2 adsorption/desorption isotherms for both biochars are IUPAC Type IV isotherms with Type H4 hysteresis loops, which are often characteristic of mesoporous structures with narrow slit-like pores or some microporosity (Figure S3).…”

“…O. chalcidica biochar was the highest-performing unmodified biochar with a plant feedstock. Additionally, the biochar outperformed 11 carbon nanotube materials specifically designed for divalent metal ion sorption. − Biochar made from O. chalcidica , which was grown on Ni-spiked potting mix and did hyperaccumulate Ni, also demonstrated high Ni­(II) sorption capacity, indicating that Ni hyperaccumulation in the feedstock does not prevent Ni­(II) sorption …”

“…Bailey and Odontarrhena bertolonii (Desv.) L.Cecchi & Selvi who found that hyperaccumulated Ni led to increased biochar production and our group working with Odontarrhena chalcidica (Janka) Španiel, Al-Shehbaz, D.A.German & Marhold (formerly known as Alyssum murale ). , …”

“…Agromining, or “farming for metals”, uses hyperaccumulator plants to concentrate metals from soil, harvests the plants, ashes the biomass to make bio-ore, and extracts the metals to make metal or metal products . Our group’s previous work focused on synthesizing an enhanced bio-ore by pyrolyzing O. chalcidica biomass into biochar and sorbing aqueous Ni from solution to it . The previous biochar study demonstrated high Ni sorption capacity, especially in biochar formed at high pyrolysis temperature.…”

“…L.Cecchi & Selvi who found that hyperaccumulated Ni led to increased biochar production and our group working with Odontarrhena chalcidica (Janka) S ̌paniel, Al-Shehbaz, D.A.German & Marhold (formerly known as Alyssum murale). 13,17 O. chalcidica is a perennial Ni hyperaccumulator native to ultramafic soils in the Mediterranean region that is known to hyperaccumulate Ni from soils with sufficient phytoavailable Ni even when planted outside of its native range. 18,19 It is known to selectively accumulate up to 30% Ca by dry weight in leaf trichomes, primarily as a carbonate or oxalate, and to accumulate Ca from soils with low Ca concentrations, which could increase the alkalinity and cation exchange capacity of any biochar made from the plant.…”