Current　studies　of　chromium　adsorption　kinetics　at　the　solid–liquid　interface　often　neglect　the　influence　of　coexisting　ions　in　complex　wastewaters.　Thus,　it　is　critical　to　explore　the　hexavalent　chromium　Cr(VI)　adsorption　kinetics　of　solid-phase　brucite　(Mg(OH)2)　in　liquid-phase　wastewater　containing　coexisting　aluminum　ions　(Al(III)).　This　paper　reveals　that　the　presence　of　Al(III)　significantly　enhanced　the　Cr(VI)　adsorption　efficiency　onto　Mg(OH)2,　with　a　peak　of　up　to　91%　compared　to　5%　for　the　absence　of　Al(III).　The　main　reason　for　this　enhancement　was　the　initial　surface　ternary　complexation　of　Mg(OH)2　and　the　cationic　(Al(III))　isomorphic　substitution　to　form　Mg(II)-Al(III)　layered　double　hydroxides　(LDH),　which　also　indicates　a　solid-phase　transition　on　the　surface　of　Mg(OH)2,　which　led　to　electrostatic　adsorption　in　the　gallery　and　made　Cr(VI)　immobilized　and　not　readily　released.　Further　calculation　and　analysis　of　the　adsorption　energy　confirmed　the　mechanism　of　Cr(VI)　adsorption.　It　was　also　concluded　that　Cr(VI)　migration　in　Mg(OH)2-containing　minerals　was　affected　by　the　phase　transformation　of　solids　in　the　presence　of　Al(III).　Hence,　this　study　not　only　reveals　the　adsorption　mechanism　during　the　treatment　of　composite　pollutant　wastewater　but　also　provides　the　methodological　reference　for　brucite　synergistic　adsorption　to　remove　heavy　metal　ions　and　purify　and　treat　complex　polluted　wastewater.　©　2023　by　the　authors.