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 m2/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.
Highlights
Steel is the most widely used metal in the world.[1]
Adsorption capacities are specific to experimental conditions such as metal mix in solution, temperature, and pH, these results suggest that the maximum observed adsorptions (Table 3) are comparable to other promising adsorbents in the literature, which range between 1 and 90 mg Ni g−1.34,65,66 Of the 45 Ni adsorbents represented in these studies, only 11 have a higher maximum adsorption capacity than the observed adsorption of the O. chalcidica biochar
The Ni concentration of O. chalcidica biomass varies according to the Ni concentration in soil but has an upper limit likely depending on either a hyperaccumulation limit in the plant or a limiting Ni desorption rate from the soil into pore water
Summary
Steel is the most widely used metal in the world.[1]. steel is primarily composed of iron, nickel (Ni) is a primary component of making stainless steel. New Ni hyperaccumulators, especially tropical species, are being consistently discovered, but the agronomy for some known temperate species is already well-established One such species, Odontarrhena chalcidica (synonymous Alyssum murale), is a perennial originating in arid Mediterranean regions with serpentine soils including Turkey, Greece, and Albania, but it is able to grow and hyperaccumulate Ni outside its native environment.[20,21] O. chalcidica uptakes Ni primarily as Ni2+ in the roots, transports it to the leaves either in the hydrated ionic form or chelated with organic ligands, and stores Ni there.[22,23] Adding fertilizer promotes biomass growth without lowering Ni concentration.[18,24] adding organic soil amendments or cocropping legumes with O. chalcidica could eliminate the need for fertilizer in some circumstances, minimizing additional inputs to farm a metal crop.[25,26] The product of a successful metal crop is known as a “bio-ore”. Depending on the Ni concentration of the solution, the adsorption process can greatly increase the bio-ore’s Ni concentration, resulting in a Ni-enhanced bio-ore
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