Abstract
Oyster shells are considered as a byproduct or solid waste in mariculture or related food processing areas that face a major disposal problem at the landfill in coastal regions for sustainable development. Oyster shell is composed mostly of CaCO3, and it is also considered as a secondary source of calcium for various applications. In this paper, we extracted the calcium carbonate from oyster shell and used it as the source of calcium for the preparation of feed-grade monocalcium phosphate (MCP). The investigation shows that the heavy metal contents in oyster shells as well as in the synthesized MCP are extremely low, and the synthesized product meets the requirements for the European Union (EU) maximum limits applied for feed additives. The XRD, TG, and IR data analyses confirmed that the synthesized product is monocalcium phosphate.
Highlights
Oyster shells are produced mainly in the mariculture and related food processing areas
Preparation Procedure. e precipitated calcium carbonate (PCC) is first prepared from the oyster shell by the modified procedure which is briefly described as follows [7]: the ground oyster shell is heated at 1000°C for 1 h, after cooling to room temperature, the powder is dispersed into water to get a hydrated lime slurry which is filtered and the hydrated lime solution is bubbled with a flow of carbon dioxide gas until the pH of the formed slurry is about 7.0
E X-ray diffraction analysis shown in Figure 1(a) and Figure S1 in the Supporting Information (SI) indicated that the CaCO3 in oyster shell has a calcite structure (JCPDS No 86-0174) which is in good agreement with other observations [2, 13]
Summary
Oyster shells are produced mainly in the mariculture and related food processing areas. Some others used oyster shells as an alternative calcium source for calcium carbonate instead of natural limestone [1], or the preparation of calcium hydrophosphate, monocalcium phosphate monohydrate, or tricalcium phosphate [4, 5]. In these investigations, the oyster shells are mixed with phosphate species to form the target materials without any proper purification so that most of the impurities, if any, in the starting materials will be retained in the final product. E use of oyster shells as the calcium source instead of natural calcium carbonate for the preparation of feed-grade calcium phosphate will be interesting and fruitful. e oyster shells which contain a very low content of heavy metals, are generated by living animals, so they are more compatible to the animals as feed supply or additives [6]. e use of oyster shells for the preparation of feed-grade calcium phosphates will add significant value to the waste of mariculture as well as related food processing of bivalve shells
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