# A Study on the Applicability of Bio-Sulfur as a Cement Admixture
## 2 Results  
### Physico-Chemical Properties of Bio-Sulfur  
Table 1 shows the results of the analysis of the physico-chemical properties of bio-sulfur. The pH was in the approximate range of 8.0-9.0, the average salinity of bio-sulfur was 2.5%, and the salinity of the supernatant after centrifugation was 4.8%. The supernatant was slightly alkaline due to the supply of NaOH, and Na\({}^{+}\) was mostly present in a form combined with OH\({}^{-}\). Because biosulfur improves the initial strength, it appears to be a useful material for addition to cement if an appropriate mixing ratio is maintained [19; 20].  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Category** & **Range** & **Avg.** \\ \hline \multirow{3}{*}{Proximate (\%)} & Combustible & 69.2–70.2 & 69.8 \\  & Water & 22.9–23.9 & 23.2 \\  & Ash & 6.9–7.1 & 7.0 \\  & Particle size (\(\mu\)m) & & 0.04–146.8 & 11.27 \\ \multirow{2}{*}{pH} & Raw & 8.90–8.92 & 8.91 \\  & Supernatant & 8.87–8.92 & 8.9 \\ \multirow{2}{*}{Na+} & Raw & 2.5–2.7 & 2.6 \\  & Supernatant & 4.7–4.9 & 4.8 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Characteristics of Bio-sulfur.  
Figure 3 shows the particle size distribution characteristics of the microparticles in the bio-sulfur. The particle sizes of the fine particles determined by analysis were as follows: 1.75 um for Dv (10), 5.3 um for Dv (50), and 11.1 um for Dv (90). The particle sizes of the fine particles dispersed in the bio-sulfur were relatively uniform at 5.3 um, which corresponds to Dv (50), on average. This likely arose due to the sulfur, which has a relatively uniform particle size due to microbial metabolism. In general, it has been reported that cement develops higher reactivity as the content of particles 10 um in size or less increases, as this results in faster setting times and increased heat of hydration due to rapid hydration [21].  
Table 2 shows the results of quantitative analysis of the constituents using XRF (X-ray fluorescence) after the bio-sulfur was dried at 100 \({}^{\circ}\)C. Sulfur, the main component of bio-sulfur, was found to exist at the highest level, at 86.8%. In addition, Na\({}^{+}\) (2.14%) and O\({}_{2}\) (9.92%) were found. Bio-sulfur contains oxygen in addition to the sulfur component because oxygen is contained in the air supplied to the sulfated bacteria during the process of converting H\({}_{2}\)S to sulfur. In addition, C (1.14%) is presumed to derive from microorganisms remaining in the bio-sulfur or from polycyclic aromatic hydrocarbons (PAHs) contained in the LFG. Due to the presence of PAHs, potential use in construction is limited given the possibilities of sick house syndrome and multiple chemical sensitivity (MCS) due to indoor air pollution [22].  
Figure 4 shows the XRD (X-ray diffraction) peak, which shows the crystal structures of the bio-sulfur and petroleum sulfur dried at 100 \({}^{\circ}\)C. It was confirmed that the petroleum sulfur was composed of S\({}^{8}\), which has a stable bonding structure as a single sulfur structure; the structure of the sulfur contained in bio-sulfur was also found to be S\({}^{8}\) and thus had the same bonding structure as the petroleum sulfur. In conclusion, from a qualitative standpoint, the petroleum sulfur and bio-sulfur are the same type of sulfur (S\({}^{8}\)), and it is considered that this product can be used as a substitute for petroleum sulfur.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Division** & **S** & **O** & **C** & **Na\({}^{+}\)** & **Total** \\ \hline Content (wt.\%) & 86.8 & 9.92 & 1.14 & 2.14 & 100 \\ \hline \hline \end{tabular}
\end{table}
Table 2: The results of quantitative analysis of the constituents using XRF.  
Figure 3: Particle size distribution in bio-sulfur. Dv is volume-average diameter. (**a**,**b**) is shows each the distribution and the cumulative distribution of particle size. The graph indicates that the area under 10 um occupies 90% of the total size distribution.