## 3 Results and Discussion  
### Characterisation of Biosorbents  
The biosorbents were characterized prior to testing to assess their varying compositions. Table 1 presents the ultimate and proximate analyses, tap and true densities, and surface characteristics (surface area and micro-pore volume) of the biosorbents. From the proximate analysis data, there is a wide range of volatile matter, fixed carbon, and ash compositions for the selected biosorbents. CH and HH had similar proximate analysis, as did RS and WW, but LD had much lower volatile contents (54.7%) and higher carbon content (29.1%). The ranking of the samples by carbon content was LD \(>\) CH \(>\) HH \(>\) RS \(>\) WW. As fixed carbon content increases, the volatile matter content decreases, as noted by numerous previous studies [71, 72, 73]. Biosorbents follow a similar trend to the volatile matter results in the ultimate analysis results (Table 1). RS had the highest carbon content (56 wt.%) and LD the lowest (29 wt.%). Among these biosorbents, LD has a higher ash content (~7.4 wt.%) than the other biosorbents, while HH, CH, and RS were about half that of LD (~3.6-4.2 wt.%). WW had a very low ash content of 0.44 wt.%. LD had the highest tap density (0.83 g/cm\({}^{3}\)) and \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline  & \multicolumn{3}{c}{**Ultimate Analysis**} & \multicolumn{3}{c}{**Proximate Analysis \({}^{\rm c}\)**} & \multicolumn{3}{c}{**Densities**} & \multicolumn{3}{c}{**Surface Area**} & **Pore Volume** \\
**Biosorbent** & \multicolumn{3}{c}{**(wt.\%, daf) \({}^{\ast}\)**} & \multicolumn{3}{c}{**(wt.\%, ar \({}^{\ddagger}\))**} & \multicolumn{3}{c}{**(g/cm\({}^{3}\))**} & **(m\({}^{2}\)/g)** & *** (cm\({}^{2}\)/g)** \\  & **C** & **H** & **N** & **O** & **b** & **MC** & **VM** & **FC** & **Ash** & **True** & **Top** & \\ \hline LD & 29.58 & 5.34 & 2.06 & 63.02 & 9.2 & 54.7 & 29.1 & 7.4 & 1.62 & 0.83 & 25.0 & 0.0091 \\ CH & 43.15 & 6.20 & 0.38 & 50.26 & 8.6 & 62.0 & 25.5 & 3.9 & 1.47 & 0.17 & 24.6 & 0.0090 \\ HH & 43.31 & 5.88 & 0.88 & 49.92 & 8.9 & 64.1 & 22.8 & 4.3 & 1.50 & 0.46 & 26.9 & 0.0098 \\ RS & 56.08 & 8.49 & 2.51 & 32.93 & 5.9 & 79.3 & 12.2 & 3.7 & 1.18 & 0.39 & 23.5 & 0.0086 \\ WW & 46.42 & 6.62 & 0.29 & 46.66 & 6.7 & 79.3 & 11.6 & 0.4 & 1.47 & 0.30 & 27.4 & 0.0100 \\ \hline \end{tabular}
\end{table} 
Table 1: Ultimate analysis, proximate analysis, true and tap densities, surface area, and micropore volume of biosorbents for seaweed (LD), natural residue (CH), agricultural residue (RS), lignocellulosic waste (HH), and waste wood (WW). NB \({}^{\rm a}\) Dry ash free basis (daf). \({}^{\rm b}\) Oxygen content by difference. \({}^{\rm c}\) MC: moisture content, VM: volatile matter, FC: fixed carbon. \({}^{\rm d}\) As received (ar). \({}^{\rm e}\) micro-pore volume. true density (1.62 g/cm\({}^{3}\)) in comparison to other biosorbents. The lowest tap density was recorded for CH (0.17 g/cm\({}^{3}\)), and RS had the lowest true density (1.18 g/cm\({}^{3}\)). Regarding surface structure, WW had the highest surface area (27.35 m\({}^{2}\)/g) and micro-pore volume (0.01 m\({}^{3}\)/g). The FTIR results show similar characterisitc peaks for all samples, but the intensity of the peaks varies (Figure 1). The wide band from 3100 to 3600 cm\({}^{-1}\) was associated with the hydrogen-bonded hydroxyl group in addition to the potential overlapping of -NH with -OH bonds (Figure 1) [74; 75]. This band is potentially due to symmetric and asymmetric stretching vibrations of H\({}_{2}\)O molecules [76; 77] and/or non-bounded -OH groups such as alcohols, carboxylic acid, and/or phenolic compounds [78; 79]. The differences in biosorbents could also explain the shifting of the peak point of the band (3100-3600 cm\({}^{-1}\)) in Figure 1.  
The peaks at 3016 cm\({}^{-1}\), 2935 cm\({}^{-1}\), and 2846 cm\({}^{-1}\) are associated with the aromatic C-H, asymmetric C-H, and symmetric C-H stretching resulting from the aliphatic functional groups [78; 80] in the biomass feedstocks.