Influence of Gluconic Acid on Dissolution of Si, P and Fe from Steelmaking Slag with Different Composition into Seawater

Abstract

In order to continuously supply nutrient elements such as Si, P and Fe into seawater for the multiplication of phytoplankton, steelmaking slag has always been utilized at coast. Yet Fe as the obligatory micronutrient element shows an extremely low solubility under the natural seawater condition. As one kind of the broadly existing organic ligands, gluconic acid is able to form a complex with iron in alkaline aqueous solution, by which the soluble iron will be stabilized and thus the solubility of iron will be improved. In the current research, the influence of gluconic acid on the dissolution of Si, P and Fe as well as the variation of pH was investigated by using shaking experiment. Present results show that gluconic acid has little effect on the variation of pH and the increase of the dissolved Si and P concentrations, whereas gluconic acid enhances the dissolution of Fe greatly by forming the iron-gluconate complexes. However, the photoreduction reaction of iron-gluconate complex occurred during shaking in the day time results in a slight decline of the concentration of the soluble iron.

Enhancement of the Dissolution of Nutrient Elements from Steelmaking Slag into Seawater by Gluconic Acid

“…In the case of slag S-2, the variation of pH with the gluconic acid concentration was not obvious, whereas pH was slightly higher than that without addition of gluconic acid. The pH of solution with slag S-2 was much higher than that of slag S-1, which is the same as that in the previous work [13]. Figure 3 shows the dissolution behavior of Ca from slags S-1 and S-2 into seawater with various concentrations of gluconic acid.…”

“…For both slags, pH increased dramatically in the beginning; however, for prolonged shaking time, the pH increase was only moderate for slag S-1 and stable around 10.1 for slag S-2. As illustrated in our previous work [13], the buffering action provided by the dissociation of gluconic acid is negligible. In the case of slag S-1, pH increased with increase of concentration of gluconic acid.…”

“…For slag S-1, ferrous ion and gluconate ion form complex as reaction (10) suggests [20]. For slag S-2, ferric ion and gluconate ion form a series of complexes with the increase of pH according to the following reactions (11)(12)(13)(14) [17,[19][20][21]: At higher pH regime, Fe 3? hardly exists, and it is prone to turn into Fe(GH)and Fe(GH)(OH) 2anions, and thus the concentration of Fe with slag S-2 is smaller than that with slag S-1.…”

“…hardly exists, and it is prone to turn into Fe(GH)and Fe(GH)(OH) 2anions, and thus the concentration of Fe with slag S-2 is smaller than that with slag S-1. On the other hand, the equilibrium constants of ferric-gluconate complexation reactions (11)(12)(13)(14) decrease with increasing pH, which is another reason for the gradual decrease of soluble Fe with increase in shaking time. In addition, the ferric-gluconate complex is photoactive at large pH condition.…”

Dissolution Mechanisms of Steelmaking Slag–Dredged Soil Mixture into Seawater

“…However, the solubility of iron in oxic seawater is extremely small at the normal pH range [5] and the dissolution of iron from steelmaking slag is significantly little. Some previous works clarified that organic acids such as gluconic acid acted as a sequestering agent for metal ions in alkaline solution and enhanced the dissolution of iron to keep the soluble iron stable in seawater [6][7][8][9]. However, the liquid organic acids are difficult to be used directly at the sea coast in a practical application, and thus, an appropriate substitute is required.…”