Abstract: The content of heavy metals in Pacific oyster shells was determined by inductively coupled plasma mass spectrometry (ICP-MS), confirming its potential as an excellent calcium source. This material was used to prepare calcium-chelating L-aspartate after being subjected to different pretreatments. The optimal pretreatment was selected based on the chelation efficiency and the product yield, and the resulting powder was fractionated by sieving. The preparation conditions including pH, temperature, time and molar ratio between L-aspartate and Ca2+ were optimized by one-factor-at-a-time and orthogonal array design methods. The obtained chelate was characterized by energy disperse spectrometry (EDS). The results showed that the chelating efficiency of oyster shell powder prepared by sequential grinding and sieving was higher than that of calcined and ball-milled shell powders. The fraction passing through 300–200 had the highest chelating rate with L-aspartate. The optimal conditions for preparing calcium-chelating L-aspartate were determined as follows: pH 4.5, 50 ℃, 100 min, and molar ratio of L-aspartate to Ca2+ 2:1. Under these condition, the chelation rate was as high as 98.5%. According to their scanning electron micrographs (SEM) and BET specific surface area characterization, the morphology of calcined, sieved and ball-milled shell powders was quite different, and their specific surface area increased in that order, corresponding to their respective chelation rates. The EDS results showed that calcium was successfully chelated to L-aspartate. This research provides a theoretical basis and new ideas for the value-added utilization of oyster shell waste and the production of calcium-chelating L-aspartate.

Key words: oyster shell, processing methods, calcium-chelating L-aspartate, process optimization