Sulfuric　acid　method　can　effectively　extract　lithium　from　lepidolite.　However,　purification　problems　make　the　method　still　tough　before　being　widely　applied.　Especially,　a　considerable　amount　of　Al3+　is　contained　in　leaching　solution,　which　needs　to　be　removed　before　Li2CO3　precipitation.　Based　on　the　characteristic　that　K+,　Rb+,　and　Cs+　can　form　corresponding　alums　with　Al3+,　an　alum　crystallization　method　was　introduced　and　applied　in　our　research.　The　feasibility　of　this　method　was　also　verified　by　phase　equilibrium　investigations　in　Li2SO4-K2SO4-Al2(SO4)3-H2O　and　its　subternary　system,　which　were　typical　subsystems　of　leaching　solution.　The　results　showed　that　Al2(SO4)3　can　form　potassium　alum　(KAl(SO4)2·12H2O)　with　K2SO4　easily,　while　no　alum　or　double　salt　was　found　between　Li2SO4　and　Al2(SO4)3.　Although　Li2SO4　can　generate　KLiSO4　with　K2SO4,　the　crystallization　of　KAl(SO4)2·12H2O　still　has　priority　over　KLiSO4　when　K2SO4　concentration　is　relatively　low.　Therefore,　aluminum　probably　can　be　removed　by　regulating　the　concentration　of　leaching　solution　located　in　the　crystallization　field　of　KAl(SO4)2·12H2O.　Besides,　the　effects　of　controlling　factors　specifically　temperature,　pH,　and　molar　ratio　of　K+/Al3+　(m　(K+/Al3+))　on　alum　crystallization　were　investigated.　The　results　indicated　that　lower　temperature　and　the　addition　of　K2SO4　can　accelerate　the　removal　of　Al2(SO4)3　obviously.　The　alum　crystallization　method　turned　out　to　be　effective　such　that　about　78　pct　of　Al2(SO4)3　can　be　removed　mainly　as　potassium　alum　(KAl(SO4)2·12H2O)　at　278　K　(5 °C)　with　m　(K+/Al3+)　at　0.9　and　pH　of　2.　A　slight　loss　of　lithium　was　caused　by　entrainment　during　alum　crystallization.　This　research　can　be　a　promising　exploration　to　purify　leaching　solution　of　lepidolite　or　other　aluminosilicates.　©　2016,　The　Minerals,　Metals　&　Materials　Society　and　ASM　International.