Because of the low cost, sufficient quantity, sufficient mineral concentration, and ionic properties, slag is the best source of this kind of mineral. Table 1 lists the best growth condition of different types of microalgae. Researchers have found that when relatively low concentration of slag or leaching solution of slag was added into an aquatic environment, the kinds of microalgae whose growth could be promoted were _Thalassiosira guilladii_ (the best addition concentration of slag was 33 mg/L [21]). _Chaetoceros gracile_ (the best addition ratio of leaching solution of slag was 20-40% [22]). _Rhodomonas lens_ (the best addition ratio of leaching solution of slag was 20-40% [22]), _Emilania luxleyi_ (the best addition ratio of leaching solution of slag was 20-40% [22]), and _Chorella_ sp. (the best addition concentration of slag 25 mg/L [23] and the best addition ratio of leaching solution of slag was 30% [24]). When a relatively high concentration of slag or leaching solution of slag was added into the aquatic environment, the kinds of microalgae whose growth could be promoted were _Skeletonema costatum_ (the best addition concentration of slag was 100 mg/L [25] and the best addition ratio of leaching solution of slag was 40-80% [20; 22]), _Thalassiosira alleini_ (the best addition ratio of leaching solution of slag was 40-80% [22]), _Isochrysis galbana_ (the best addition ratio of leaching solution of slag was 40-80% [22]), _Thalassiosira angulate_ (the best addition ratio of leaching solution of slag was 100% [22]) and _Amplidinium carterae_ (the best addition ratio of leaching solution of slag was 100% [22]). When an arbitrary concentration of slag or leaching solution of slag was added into the aquatic environment, the kinds of microalgae whose growth could be promoted were _Dunaliella tertiolecta_ [22], _Tetraselmis tetrathele_ [22], _Synechococcus_ sp. [22], _Desmodesmus subpicatus_ [26], _Chlorella vulgaris_ [26], _Alexandrium tamarense_ [25], and _Nitzeschia laevis_ [27]. Nevertheless, in spite of the research and explorations on the effects of slag on the growth of microalgae, the reason for the influence of steel slag leaching solution on the growth of microalgae was still unclear. \begin{table}
\begin{tabular}{c c c c} \hline
**Types of Microalgae** & **Types of Growth Condition** & **Best Growth Condition** & **Reference** \\ \hline _Thalassiosira guilladii_ & Slag & 33 mg/L & [21] \\ \hline _Chaetoceros gracile_ & Leaching Solution of Slag & 20 vol\%–40 vol\% & [22] \\ \hline _Rhodomonas lens_ & Leaching Solution of Slag & 20 vol\%–40 vol\% & [22] \\ \hline _Emilania luxleyi_ & Leaching Solution of Slag & 20 vol\%–40 vol\% & [22] \\ \hline _Chlorella_ sp. & Slag & 25 mg/L & [23] \\ \hline _Skeletonema costatum_ & Slag & 30 vol\% & [24] \\ \hline \end{tabular}
\end{table} 
Table 1: The best growth condition of microalgae. This research selects converter slag and electric arc furnace slag as representatives, which are commonly used in the process of steelmaking, and aims to study effects and mechanisms of converter slag and EAF slag leaching solutions on the accumulation of chlorophyll a of _Nannochloropsis_ sp. In order to compare the effects of accumulation of chlorophyll a under different adding proportions of converter slag and EAF slag leaching solutions and to explore the mechanisms of effects of steel slag leaching solution on the accumulation of chlorophyll a, different proportions of converter slag and EAF slag leaching solutions were added into F/2 medium to continuously culture _Nannochloropsis_ sp. Through various characterization means, the main components of steel slag leaching solution, the effects of accumulation of chlorophyll a of _Nannochloropsis_ sp., and the mechanisms and effects of steel slag leaching solution on the accumulation of chlorophyll a were analyzed and explained.