Since　the　leaching　solution　of　lepidolite　contained　a　great　amount　of　aluminum　after　lithium　extraction,　how　to　remove　or　recover　effectively　would　definitely　affect　the　cost　for　lithium　extraction.　The　comprehensive　analysis　was　made　on　the　merits　and　shortcomings　of　the　traditional　methods:　alkali,　acid　and　solvent　extraction　methods.　Then　a　more　effective　way　was　proposed:　recovered　aluminum　by　alums　formation　with　K+　or　other　components　contained　in　the　leaching　solution.　The　cost　for　lithium　extraction　would　be　decreased　by　producing　value　added　co-products　such　as　potassium　alum.　The　Li2SO4-　Al2(SO4)3-H2O　and　K2SO4-　Al2(SO4)3-　H2O　ternary　systems　were　the　subsystem　of　the　featured　system　of　the　leaching　solution.　The　phase　equilibria　in　the　Li2SO4-　Al2(SO4)　3-H2O　and　K2SO4-　Al2(SO4)3-H2O　ternary　systems　at　5°C　were　investigated　with　isothermal　equilibrium　method.　The　phase　equilibria　investigation　could　provide　fundamental　data　and　instruction　for　lithium　extraction,　which　was　important　for　alum　formation　to　recover　aluminum.　The　solid　phase　was　determined　by　X-ray　diffraction　(XRD)　analysis.　Based　on　the　solubility　data,　the　phase　diagrams　were　plotted.　The　crystallized　fields　also　were　determined.　The　phase　diagrams　showed　that　K2SO4　and　Al2(SO4)3　could　form　potassium　alum　(KAl(SO4)2·12H2O)　in　a　large　range　of　concentration,　while　it　seemed　that　Li2SO4　and　Al2(SO4)3　could　not　form　double　salts.　The　investigation　indicated　that　Li+　and　Al3+　could　not　form　alum,　but　K+　and　Al3+　could　form　potassium　alum　easily.　Therefore,　the　aluminum　could　be　recovered　by　regulating　K+,　Li+　and　Al3+　concentration　to　form　alums.　Thus,　the　aluminum　was　recovered　as　high　value　co-products,　and　lithium　and　potassium　could　be　separated　preliminarily.　The　alum　formation　method　could　decrease　costs　and　enlarge　profit　for　lithium　extraction,　which　had　significant　practical　meaning　for　lithium　extraction.