Pyropia haitanensis (P. haitanensis) is a commercially significant alga in China, and the vitality of its industry is closely associated with coastal economic stability and food safety. Intensifying coastal pollution and deteriorating aquaculture conditions have exacerbated heavy metal accumulation in P. haitanensis, threatening sustainable development and limiting industry viability. Conventional processing methods exhibit substantial limitations in heavy metal removal, nutrient retention, and preservation of algal tissue structure, restricting their ability to meet market demands. To address this challenge, we developed a synergistic ultrasound-assisted citric acid treatment technology. In this process, ultrasound facilitates the release of heavy metal from algal tissue, while citric acid chelates and removes them, termed the “Release–Chelation” effect. The approach aims to efficiently remove heavy metal while maintaining P. haitanensis quality and nutritional value. Under optimized conditions of citric acid concentration, sonication time, and power, heavy metal residues were effectively reduced below national regulatory standards. SEM and FT-IR analyses indicate that removal occurs with minimal structural damage. Nutritional analyses revealed slight reductions in crude protein and amino acid content, yet overall nutritional quality remained satisfactory. These results demonstrate that the technology preserves the edible value of P. haitanensis while efficiently removing heavy metals, highlighting its potential to advance the algae industry toward safer and more sustainable practices.