## 3 Results and Discussion
### Effects of Steel slag Leading Solution on Accumulation of Chlorophyll A  
The content of chlorophyll a, one of the indexes reflexing growth of microalgae, is usually used to measure the growth of microalgae. The increase of chlorophyll a fluorescence value in vivo in microalgae means that growth of microalgae is promoted, while the decrease means it is inhibited [28]. The chlorophyll a method is usually used to measure the biomass of microalgae. There is a significant positive correlation between chlorophyll a and biomass [29]. Thus, biomass increases with the increase of content of chlorophyll a. Figure 2 shows the relations between concentration of chlorophyll a of _Nannochloropsis_ sp. and addition of converter slag leaching solution. Results show that when the addition of converter slag leaching solution was less than 50 vol%, concentrations of chlorophyll a added to converter slag leaching solution were higher than that of control group. Concentration of chlorophyll a decreased with the increase of addition of converter slag leaching solution. Thus, when addition of converter slag leaching solution was less than 50 vol%, accumulation of chlorophyll a of _Nannochloropsis_ sp. could be promoted. The promoting effect decreased with the increase of addition of converter slag leaching solution. When the addition of converter slag leaching solution was 10 vol%, the concentration of chlorophyll a reached the highest (4.2 mg/L), 1.45 times as much as that of control group, so when addition of converter slag leaching solution was 10 vol%, the promoting effect was the best. When the addition of converter slag leaching solution was 70 vol%, the concentration of chlorophyll a was lower than that of the control group, so under this addition, accumulation of chlorophyll a of _Nannochloropsis_ sp. was inhibited. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Main Elements in Slag**} & **Converter Slag** & **EAF Slag Leaching** & **Waste Synthetical** & **Standard of Drinking** \\  & **Leaching Solution** & **Solution** & **Discharge Standard a** & **Water for Life b** \\ \hline Total Mg & 5.1 \(\times\) 10\({}^{-2}\) & 1.8 \(\times\) 10\({}^{-1}\) & & 4.5 \(\times\) 10\({}^{2}\) \\ Total Al & 1.2 \(\times\) 10\({}^{-2}\) & 3.1 \(\times\) 10\({}^{-2}\) & & 0.2 \\ Total Ca & 5.6 & 2.2 & & 4.5 \(\times\) 10\({}^{2}\) \\ Total Fe & 0.8 \(\times\) 10\({}^{-3}\) & 0.4 \(\times\) 10\({}^{-3}\) & & 0.3 \\ Cr (VI) & 0.1 \(\times\) 10\({}^{-4}\) & 0.7 \(\times\) 10\({}^{-4}\) & 0.5 & 0.5 \(\times\) 10\({}^{-1}\) \\ Total Mn & 0.1 \(\times\) 10\({}^{-2}\) & 3.9 \(\times\) 10\({}^{-2}\) & 0.1 & 0.1 \\ Total V & 6.8 \(\times\) 10\({}^{-2}\) & 0.1 \(\times\) 10\({}^{-3}\) & & \\ Total P & 5.1 \(\times\) 10\({}^{-2}\) & 0.8 \(\times\) 10\({}^{-3}\) & 0.5 & \\ \hline \hline \end{tabular}  
* Reference Standard: GB 8978-1996. b Reference Standard: GB 5749-2006.  
\end{table} 
Table 6: Concentrations of main elements in converter slag and EAF slag leaching solutions, (mg/L). Figure 3 shows the relations between the concentration of chlorophyll a of _Nanochloropsis_ sp. and the addition of EAF slag leaching solution. Results show that when the addition of EAF slag leaching solution was less than 50 vol%, concentrations of chlorophyll a added to EAF slag leaching solution were higher than that of control group. The concentration of chlorophyll a decreased with the increase of amount of EAF slag leaching solution added. Thus, when the addition of EAF slag leaching solution was less than 50 vol%, accumulation of chlorophyll a of _Nanochloropsis_ sp. was promoted. The promoting effect decreased with the increase of addition of EAF slag leaching solution. When addition of EAF slag leaching solution was 10 vol%, the concentration of chlorophyll a reached its highest level (3.2 mg/L), 1.10 times as much as that of control group, so when addition amount of EAF slag leaching solution was 10 vol%, the promoting effect was the best.