Data for: Feedstock nitrogen content mediates maximum possible Pb sorption capacity of biochars

Biochars were produced from four different feedstock materials: hay, wheat straw, coco coir, and pine bark. The feedstock materials were packed in steel containers with a small hole cut into the lid to avoid pressure build up. The containers were heated to the desired temperature for one hour using a Gallenkamp Muffle furnace to pyrolyse the feedstocks and then allowed to cool overnight before the biochar was removed. Biochars were made from each of the four feedstocks at 300 °C, 350 °C, 400 °C, 450 °C, 500 °C, 550 °C, 600 °C, 650 °C, 700 °C, and 750 °C, resulting in a total of 40 different biochars. The biochars were each ground to a fine powder using a TEMA T100ACH Laboratory Disc Mill.

Biochar pH was determined in triplicate by shaking 1g of biochar with 20ml of ultra-pure water for 30 minutes and measuring the pH of the biochar/water slurry. Approximately 4 mg of each ground biochar and feedstock sample was analysed for total carbon and nitrogen content by dry combustion using a Thermo Scientific Flash 2000 Organic Elemental Analyser. Biochars and feedstocks were digested in nitric acid prior to determination of Ca, Mg, K, P, S, Na, Cu, Pb, Mn, Zn, Al, and Fe by the ICP-OES (Inductively Coupled Plasma Optical Emission Spectroscopy).

Pb batch adsorption isotherms were carried out for each of the 40 biochars using five Pb solutions (100, 200, 500, 1000, and 5000 mg Pb L-1) prepared by serial dilution of a 5000 mg L-1 stock solution of lead nitrate made by dissolving Analytical grade Pb (NO3)2 in > 18.2 MΩ.cm water. Milled biochar (1 g ± 0.05 g) was weighed into a 50 ml centrifuge tube and 30 ml of Pb solution was added to each sample. Samples were placed in a rotary end-over-end shaker at 20 inversions per minute, at a controlled temperature of 20 °C for 24 hours for to ensure equilibrium between biochar surfaces and the Pb in solution. After 24 hours, samples were removed from the shaker and the pH was measured and recorded. Samples were then centrifuged at 3600 rpm for 15 minutes to separate the biochar particles from solution using a Mistral 3000i centrifuge. The supernatant was filtered through a Whatman no. 5 filter paper. Further filtration was carried out using a 0.2 µm cellulose membrane syringe filter. Samples were then diluted and acidified using concentrated nitric acid (HNO3) and analysed for Pb concentration using an ICP-OES.
Cs is the Pb concentration on biochar (mg g-1), Ci is the initial solution Pb concentration (mg L-1), Caq is the final solution Pb concentration (mg L-1), V is the solution volume (L), and Sm is the mass of biochar (g).