Suppression of phosphate liberation from sediment by using iron slag

Abstract

In order to suppress the phosphate liberation from sediment to sea water, several suppressing materials such as four kinds of iron slag, river and sea sands, and glass bead were tested. The sediment and sea water were sampled from Hiroshima Bay which seemed to be a eutrophicated area. The suppressing materials were covered on the surface of sediment, and sea water was introduced in the aquarium. The concentrations of phosphate, sulfide and dissolved oxygen were measured during the incubation period under the condition of anaerobic state. The suppressing effects of slags, sea and river sands were compared with that of glass bead used as control materials, and the suppression efficiencies were measured. The suppression efficiency of glass bead was 54.1%, and those of slag-2, -3 and -4 were 97.3, 96.1 and 98.8%, respectively. The suppression efficiency depended on the amounts of slag used, and about 85% of liberated phosphate were suppressed by slag-3 of 7.5 kg m −2. The sulphide ion generated under anaerobic state reacted with some metals on the surface of slags and sands, and the dissolution of precipitated phosphate (Fe-P, Al-P and Ca-P) was suppressed by formation of metal sulfide on the surface of slags and sands. The suppression mechanisms on phosphate liberation, such as covering, chemical and adsorption effects were proposed and discussed. The suppression by slag was mainly carried out by the adsorption effect, in addition to the covering effect.