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The extraction of Ni2+ and Pb2+ ions from aqueous medium using unmodified (ROSE) and the 4-aminophenol modified red onion skin extract (ROSEDS) has been successfully achieved. Cold solvent extraction technique using a 50:50 acetone/water ratio was used for extraction of the red onion skin at 125 µm mesh size. The metal concentrations were determined using Atomic Absorption Spectrometry technique. Optimum percentage removal of the metal ions was achieved at pH 6.26 for Ni2+ (89.40 % for ROSE and 97.60 % for ROSEDS) and pH 7.57 for Pb2+ (80.10 % for ROSE and 82.56 % for ROSEDS). Optimum adsorption capacities of ROSE and ROSEDS for Ni2+ were 6.30 mg/g and 7.10 mg/g respectively; while for Pb2+ ions, values obtained for ROSE and ROSEDS were 5.87 mg/g and 6.34 mg/g respectively. Varying adsorbents dosage at fixed metals ion concentration yielded optimum percentage removal of 89.90 % and 97.90 % for Ni2+, while 86.85 % and 90.80 % for Pb2+, using ROSE and ROSEDS, respectively. Adsorption capacities of the adsorbents varied inversely with adsorbent dosages. In general, 4-aminophenol modified red onion skin extract (ROSEDS) gave comparatively, better results for the extraction of Ni2+ and Pb2+ ions from aqueous medium; relative to the unmodified red onion skin extract (ROSE). Additionally, extraction of Ni2+ ions gave higher percentage removal values in both adsorbents when compared to extraction of Pb2+ ion under similar conditions. This result has been attributed to differences in their ionic radii. REVIEW ARTICLE | April 4, 2023

In this study, kola-nut testa samples were modified with 0.1 M acetic acid and 0.1 M EDTA at room temperature. The modified Kola-nut testa samples were then characterized with respect to their pH at point of zero charge, melting point, specific gravity, Fourier-transform infrared (FTIR) spectra, and solubility. The characterization results of the modified Kola-nut testa (MKT) revealed that it was sparingly soluble in water, ethanol, and acetone but insoluble in n-hexane. The MKT had a specific gravity of 0.992 ± 0.020 and exhibited various pH values of 4.50 ± 0.50 and 12.00 ± 0.50 at the point of zero charges. The FTIR spectra of the MKT indicated the presence of –OH and –NH groups at 3310.97 cm−1, alkyl groups at 2928.53 cm−1, and aromatic rings at 1612.27–1529.81 cm−1. The results of the adsorption studies at various time intervals indicated that MKT had the capacity to adsorb Fe2+, Mg2+, Zn2+, Cu2+, and Pb2+ as follows: 1.90 ± 0.30 mg/g, 1.80 ± 0.20 mg/g, 1.40 ± 0.20 mg/g, 0.10 ± 0.01 mg/g, and 0.05 ± 0.01 mg/g, respectively. Thus, Fe2+, Mg2+, and Zn2+ were quantitatively removed from the aqueous solutions, whereas Cu2+ and Pb2+ were not. The adsorption of Fe2+, Mg2+, Zn2+, Cu2+, and Pb2+ by MKT from the aqueous medium was dependent on certain factors such as pH, temperature, adsorbent dosage, contact time, and initial metal-ion concentration.

Pot experiments were conducted to investigate the impact of chromium on nutrient uptake by fluted pumpkin (Telfairia occidentalis) in soil. The study was conducted with a sandy loam soil for three weeks on a slightly acidic soil. Stratified sampling method was used. Soil samples were collected before and after planting to determine soil nutrient concentrations using Atomic Absorption Spectrophotometer and Hach Spectrometer. The result showed a maximum uptake of 27.5%, 17.57%, 17.07%, 9.76%, 18.44% and 3.66% for N, P. Mg, Fe, Ca, and K respectively. Excellent morphological characteristics were observed at 2.5ppm chromium concentration with average height, average number of leaves and average distance between nodes as 33.0cm, 10 and 4.8cm in contrast with 21.0cm, 8 and 2.3cm respectively. The impact of chromium concentration showed no specific trend on all nutrients considered, but had varying effects on the uptake of individual nutrient. The result also showed that increasing chromium concentration inhibit the uptake of Mg, Fe, Ca and P possibly due to competition for sorption site, masking and the formation of insoluble complexes.