In this study, a “cage” strategy was developed to effectively control the dissolution of Ca2+ into water without losing F− removal rate. Specifically, calcium oxide loaded with zinc‑aluminum composite oxides was synthesized as an adsorbent using urea hydrothermal method and a high temperature calcination process with limescale waste as the precursor, which achieved high efficiency in removing fluoride (qe = 336.41 mg·g−1) while inhibiting the dissolution of Ca2+ (cCa2+=98.34 mg·L−1) in the adsorbent due to the encapsulation of calcium oxide by zinc‑aluminum oxide particles agglomerates and thus reducing the secondary pollution generated by the adsorbent. The results of batch adsorption experiments show that the adsorbent has better adsorption performance than most fluoride adsorbents and can be applied in a wide pH range (3–11) and has strong resistance to the effect of coexisting anions. The precipitate of calcium fluoride, ion exchange, electrostatic interactions and hydrogen bonding are the main adsorption mechanisms. The results of the study suggest that the calcium oxide loaded by zinc‑aluminum composite oxides synthesized from inexpensive limescale waste as precursor provides a new idea for the development of low-cost and high-efficiency fluoride adsorbents, as well as solves the problem of secondary contamination of traditional calcium-based adsorbents. Display omitted •A CaO loaded with ZnAl composite oxides is prepared with limescale as precursor.•The F− adsorption capacity of the adsorbent was higher than that of most adsorbents.•The modification of CaO by ZnAl effectively inhibited the dissolution of Ca2+.•The reuse of limescale reduces the environmental hazards of its waste.•The reuse of cheap and readily available limescale reduces the cost.