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

Abstract

Steelmaking slag has been buried in coast to provide nutrient elements, especially iron, into seawater for the seaweeds' growth. However, the solubility of iron is extremely low under the oxic seawater conditions. In order to stabilize soluble iron which is dissolved from steelmaking slag into seawater, the addition of gluconic acid was investigated in the present study. By using two kinds of synthesized steelmaking slag with different CaO/SiO 2 ratios, the effect of gluconic acid on the dissolution behavior of various elements into seawater, while varying the concentration of gluconic acid and pH, was studied. The dissolution of Ca, Si, P, and Fe was greatly enhanced by the addition of gluconic acid and their concentration increased for increasing gluconic acid concentration. The dissolution mechanisms of each element were discussed using their stability diagrams and the dissolution reactions.

Dissolution Mechanisms of Steelmaking Slag–Dredged Soil Mixture into Seawater

“…The artificial seawater is the same type as that used in our previous work [9]. The compositions are given in Table 2, and have a pH value of about 8.20 and concentrations of Ca and Mg are 418 and 1328 mg/L, respectively.…”

“…Firstly, solid complexes between ferric ion and organic acids (OAs) contained in the dredged soil are formed after mixing the slag and dredged soil as given in reaction (8). During the shaking experiment, solid complexes dissolve into seawater and photoreduction reactions under the illumination in the day time induce these solid ferric-organic acid complexes to form ferrous organic acid complexes as given in reaction (9). Due to the smaller equilibrium constants for the formation reaction of the ferrous organic acid complexes, free Fe 2?…”

“…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.…”

Alkali Elution Behavior of Steelmaking Slag Packed in an Open Channel Vessel in Seawater

“…Steelmaking slag has been utilized in ocean area as sea-grass beds due to its rich source of minerals such as iron oxide and silicon oxide [1][2][3][4][5][6][7][8][9][10][11], a usable material to prevent seawater contamination caused by sulfide contained in the bottom soil matter of the sea [12][13][14][15], and materials to increase soil strength by mixing with dredged soil or bottom materials of the sea [16,17]. However, a part of CaO in steelmaking slag exists as isolated free CaO and is decomposed into Ca 2+ and OHions in seawater.…”

Dissolution mechanisms of steelmaking slags in sea water

“…In the previous researches, the dissolution behaviour of steelmaking slag was first measured (Zhang et al 2012) and the effect of blending of steelmaking slag with dredged soil on its dissolution behaviour was studied (Zhang et al 2016). In order to understand the role of organic acid contained in dredged soil, the effect of gluconic acid addition in sea water on the slag dissolution was studied in detail (Zhang et al 2014(Zhang et al , 2015. Through the above-mentioned laboratory-scale experiments and use of their solubility diagrams, the dissolution mechanisms of nutrient elements from steelmaking slag or steelmaking slag composite material are summarized.…”