The invention relates generally to a process for the preparation of water-absorbent polymer particles, comprising the process steps of (i) preparing an aqueous monomer solution comprising at least partially neutralized, monoethylenically unsaturated monomers bearing carboxylic acid groups (α1) and at least one crosslinker (α3) (ii) optionally adding fine particles of a water-absorbent polymer or aqueous salt solutions to the aqueous monomer solution (iii) adding a polymerization initiator or at least one component of a polymerization initiator system that comprises two or more components to the aqueous monomer solution (iv) decreasing the oxygen content of the aqueous monomer solution (v) charging the aqueous monomer solution into a polymerization reactor (vi) polymerizing the monomers in the aqueous monomer solution in the polymerization reactor, thereby obtaining a polymer gel (vii) discharging the polymer gel out of the polymerization reactor and optionally comminuting the polymer gel thereby obtaining polymer gel particles (viii) drying the polymer gel particles (ix) grinding the dried polymer gel particles thereby obtaining particulate water-absorbent polymer particles (x) sizing the grinded water-absorbent polymer particles and (xi) crosslinking the surface of the grinded and sized water-absorbent polymer particles wherein process step (xi) comprises the steps of: (x1a) mixing the particles with an aqueous crosslinker solution and (x2a) heat-treating the mixture obtained in process step (x1a) in a horizontally operated mixing device, wherein the horizontally operated mixing device is hydraulically driven.本發明通常係關於一種吸水性聚合物顆粒之製備方法,其係包含以下方法步驟:(i)製備一水性單體溶液,其係包含至少部分中和(neutralized)之具有羧酸基團之單乙稀基型(monoethylenically)不飽和單體(α1)及至少一交聯劑(α3);(ii)視需要添加一吸水性聚合物之細顆粒或水性鹽溶液至該水性單體溶液;(iii)添加一聚合反應起始劑或一包含二或多種成分之聚合反應起始劑系統之至少一成分至該水性單體溶液;(iv)減少該水性單體溶液之氧含量;(v)將該水性單體溶液裝入一聚合反應器;(vi)於該聚合反應器中聚合於該水性單體溶液中的單體,以得到一聚合物凝膠;(vii)將該聚合物凝膠排出該聚合反應器,並視需要細碎該聚合物凝膠,以獲得聚合物凝膠顆粒;(viii)乾燥該聚合物凝膠顆粒;(ix)研磨該經乾燥之聚合物凝膠
