Pilot scale production of one-dimensional (FeS2)nn- rods was performed by using an automatic 20L vessel at 80°C under atmosphere condition with the resource utilization of Fe-rich sludge. The sludge was simulated at lab-scale with chemical pure of ferric trichloride. After the sludge treatment, the corresponding rods were not formed at room temperature. But by heating at 80°C, erdite rod was well-crystallized after 0.5h by only adding Na halite, and KFeS2 rod was crystallized weakly after 2h and highly at 10h with the addition of K halite. After 48h heating, the rods grow radially to 300nm for erdite, but to 5μm for KFeS2. However, at room temperature, erdite rod was converted to high crystallized KFeS2 in KOH water or ethanol solution, whilst the conversion of KFeS2 rod to erdite also occurred in NaOH water solution, but terminated in NaOH ethanol solution, without any morphology change. It is also noted that with the presence of both Na and K halite, the rod was an intermediate of erdite to KFeS2 with 1μm length after heating at 100°C but converted to 10-μm-length KFeS2 crystal at the temperature of > 120°C. The thermodynamic results confirmed that during the rod polymerization, the Fe(OH)3HS- formation was the sole rate-limiting step and showed a positive Gibbs value of 6.45kJ/mol at room temperature and negative values at the temperature of > 48°C. In summary, this method not only enabled the vaporization of waste Fe-rich sludge as value-added rods without generating any secondary waste but also showed a new route for the in situ conversion of erdite/KFeS2 rods at room temperature.
Read full abstract