Iron-rich　sludge　produced　from　the　Fenton　oxidation　process　of　pulp　and　paper　mill　wastewater　contains　high　content　of　iron,　leading　to　the　dewatering　difficulty　of　the　mixed　sludge.　To　solve　this　problem　and　reuse　the　iron-rich　sludge,　an　innovative　approach,　acidifing　the　iron-rich　sludge　to　leach　out　Fe3+as　a　sludge　conditioning　agent,　was　proposed　in　this　study.　The　composition　of　iron-rich　sludge　was　analyzed　by　elemental　analyzer,　X-ray　fluorescence　spectrometry　(XRF),　and　inductively　coupled　plasma　optical　emission　spectrometry　(ICP-OES).　The　chemical　phase　and　valence　of　iron　were　determined　by　X-ray　diffraction　(XRD)　and　X-ray　photoelectron　spectroscopy　(XPS).　The　acidification　conditions　were　optimized　according　to　the　iron　leaching　rate　and　acid　consumption.　The　performance　of　the　chemical　conditioning　agent　obtained　by　this　approach　was　estimated　according　to　the　decrease　of　sludge　specific　resistance,　and　was　compared　with　the　conditioning　performance　of　FeCl3.　The　results　indicate　that　the　iron　content　is　39.32%　in　the　iron-rich　sludge　from　a　pulp　and　paper　mill,　and　ferrihydrite　is　the　main　form　of　ferric　iron.　The　optimal　condition　for　acidification　at　room　temperature　is　that　the　mass　ratio　of　sulfuric　acid　to　dry　sludge　is　0.91　g/g　and　the　reaction　time　is　180　min.　Under　the　optimal　condition,　57.24%　of　the　iron　in　the　sludge　can　be　leached　into　the　solution.　When　the　dosage　of　conditioning　agents　made　from　iron-rich　sludge　reaches　3.45%　(by　the　mass　of　Fe)　of　dry　sludge,　the　specific　resistance　of　excess　sludge　can　be　reduced　to　17.90%　of　the　initial　value,　which　is　quite　close　to　the　conditioning　performance　of　FeCl3at　the　same　dosage.　The　results　show　that　this　proposed　method　is　a　feasible　process　for　the　recycling　of　the　iron-rich　sludge　from　pulp　and　paper　mills.　©　2016,　Editorial　Office　of　Journal　of　Xi＇an　Jiaotong　University.　All　right　reserved.