The mutual effect of steelmaking slag layer depth and diameter on alkali elution rate was investigated using two kinds of open channel vessels with straightened seawater. Seawater velocity, slag layer depth, and diameter were changed from 0.2 × 10−2 to 4.2 × 10−2 m/s, from 3.3 × 10−2 to 5.0 × 10−1 m, and from 0.10 × 10−2 to 2.18 × 10−2 m, respectively. The alkali elution rate increased with an increase in seawater velocity. The effective mass transfer coefficient, which was smaller than the true mass transfer coefficient, was calculated using the total slag surface area including the slag layer irrelevant to the alkali elution. It approached the true mass transfer coefficient when the slag diameter was larger and the slag layer was thinner. Moreover, the ratio of the effective mass transfer coefficient to the true one approached unity when the pH change in the slag layer was decreased. The slag layer height, H (m), involved in the alkali elution rate was calculated using H/d = 2.98 × 10−2 Re − 1.24 × 10−5 Re 2 when the total slag layer height, h s (m), was larger than H (m). Here, d is the slag diameter (m) and Re is the Reynolds number.

In order to understand the alkali elution behavior of steelmaking slag under continuous flow, a kinetic study was carried out by continuous stirred tank reactor (CSTR). Tap water and seawater were used for measurements of circumferential velocity and temporal change in pH, respectively. Liquid was fed into the vessel and flowed constantly during the impeller rotation operation in the vessel. The effect of the various operating factors such as vessel inner diameter, slag size, slag composition, ratio of liquid volume to mass of slag, seawater feed rate, impeller height from the slag, impeller rotation speed etc. were investigated.The circumferential velocity in the vessel was not affected by seawater feed rate but by the impeller rotation speed. The alkali elution rate increased with the increase in the circumferential velocity. The alkali elution rate was not influenced by the ratio of liquid volume to mass of slag and impeller height from the slag surface. The alkali elution rate decreased with the decrease in diameter of slag particle below 0.01 m due to the insufficient penetration of seawater between slag particles. The alkali elution rate increased with the increase in seawater feed rate at the same circumferential velocity. The non-dimensional correlation equation of alkali elution rate was shown by Sh = 8.26x10(-4)Re(p)(0.62) (N tau)(-37) where Sh: Sherwood number, Rep: Particle Reynolds number and (N tau): the product of impeller rotation speed and residence time.