Fluidized-bed type reactors are frequently used in crystallization process. In this type of reactor, suspend solids (SS) produced by primary nucleation under supersaturated condition would flow out with upward flow, resulting in high SS in the effluent. Installation of filter unit is needed to prevent suspend solids in the discharge. In this study, a novel reactor named “moving-bed reactor” having two functionalities, namely filtration and crystallization, was studied for lead (Pb) removal from aqueous solutions.
According to literatures and design parameters of moving-bed reactor, five potential factors which may affect the process performance, are indentified, including lead concentration, pH, air-flow rate, the ratio of CO32-/Pb2+ and the height of sand. A 25-1 fractional factorial design is utilized to discuss the effect of factors on Pb removal efficiency, recovery efficiency and turbidity. Lead concentration and pH are the most significant factors affecting process performance. Subsequently, RSM with CCD design are used to build regression models for removal efficiency and recovery efficiency, respectively. The best operating condition was determined by uniting two regression models with pH 8.6 and 1.45×〖10〗^(-4)M of lead concentration obtained. Under the best operation condition, Pb removal efficiency and recovery efficiency are predicted to be 100.00% and 94.90%, respectively, by regression models. However, they are only 98.75% and 87.28%, respectively, experimentally. The differences are 1.25% and 8.00%, respectively, for Pb removal efficiency and recovery efficiency. The experiment can not reach the target that models predict because prediction of models is not precise.
Based on quality analysis, crystallized Pb on the sand surface and precipitated Pb filtered by sand are 18.59% and 68.69%, respectively. The result indicated design of moving-bed reactor is inadequate to recover Pb.