水泥與水泥/不飽和聚酯複合體固定化鉻之機制

Abstract

對不同的廢棄物，尤其含重金屬之污泥，化學固定法被公認是最有效的處理技術之一 。水泥系固定化(S/S)程序具有使重金屬沈澱固化之作用，已被成功地應用在各種污泥固 化上。然依Arniella與Blythe (1990)研究指出，水泥固化體有10-5到10-9cm/sec的滲透 率，在Mindess與Young (1981)所著〝CONCRETE〞書中亦提到當水泥水化時會產生0.01到1 0(m大小的孔隙，這些孔隙形成通道，重金屬會藉此滲出，降低固定化效果。 本文研 究以水泥與水泥/不飽和聚酯複合體固定化含鉻污泥之反應機制。在水泥中加入不飽和聚 酯(UP)作固化體加強劑，使產生聚合或交聯作用，改善水泥滲透之缺點，提昇水泥系固定 化效果。使用的固化劑有水泥、水泥/不飽和聚酯及水泥單礦物((-C2S、C3S、C3A)。採用 的廢棄物有含鉻污泥、三氧化二鉻及硝酸鉻。應用掃描式電子顯微鏡(SEM)、X光能量散佈 儀(EDS)、X光繞射儀(XRD) 、固態核磁共振儀(29Si、27Al MAS/NMR)等精密儀器做結構及 分子分析，使用單軸抗壓強度(UCS)做巨觀分析，並運用毒物特性溶出程序(TCLP)做溶出 試驗。設計三個主要固定化反應程序，主要結論如下：一、水泥與水泥/不飽和聚酯複合 體固定化含鉻污泥之反應程序1. 水泥固定化含鉻污泥，其單軸抗壓強度大於10 Kg/cm2與 毒性物質溶出量皆符合我國衛生掩埋標準，但需分區獨立管理。2. 水泥/不飽和聚酯固 定化含鉻污泥，其單軸抗壓強度大於150 Kg/cm2與毒性物質溶出量大部份符合我國回收再 利用之條件。3. 水泥固化系試體之顯微結構呈現鬆散的組織；而水泥/不飽和聚酯固化 系試體之顯微結構呈現緊密的網狀組織。二、水泥或水泥/不飽和聚酯複合體固定化Cr2O3 或Cr(NO3)3 □9H2O之反應程序1. Cr2O3/Cement試體能形成CaCrO4結晶相，歸因於在水化 水泥產物中，Cr可能有取代Si的現象。2. 水泥固定化硝酸鉻，水泥水化程度會下降，而 水泥/不飽和聚酯固定化硝酸鉻，水化程度會明顯下降，表示硝酸鉻與不飽和聚酯皆會阻 礙水泥水化程度。三、水泥單礦物((-C2S、C3S、C3A)固定化Cr(NO3)3 □9H2O之反應機制 1. 水化(-C2S固定化硝酸鉻，會形成(-CaCrO4□2H2O新結晶相，表示Cr可能取代Si。2. 水化C3S固定化硝酸鉻，會形成CaCrSi4O10、CaCrO4 □2H2O及CaCr2O7三種新結晶相，表 示Cr可能取代Si。3. 水化C3A固定化硝酸鉻，會形成Al2(OH)4CrO4新結晶相，表示Cr與Al 會相互作用。 Chemical fixation/solidification of wastes is one of the best demonstrated a vailable technologies for treating wastes, especially those containing heavy m etals. Cement-based solidification/stabilization (S/S) processes have proven s uccessful on many sludges generated by the precipitation of heavy metals. Cement-based waste forms, however, typically have a permeability value rangin g from 10-5 to 10-9 cm/sec. The capillary pores, which serve as a trans-portat ion conduit, have sizes ranging from 0.01 to 10(m in the hydrated cementpaste, thereby decreasing the effectiveness of solidification/stabilization. The p resent study is to investigate the mechanisms of solidification/ stabilization of chromium with cement and cement/unsaturated polyester com- posite. When un saturated polyester (UP) is added as modification, the cement/ UP causes polym erization or crosslinking, thus reducing the permeability of treated wastes an d improving the effectiveness of solidification/stabili-zation of wastes. Th e fixing agents used include cement, cement/UP and cement constituents (i.e. ( -C2S, C3S, and C3A). The wastes were chromium-containing sludge, chromic oxid e (Cr2O3) and chromium nitrate (Cr(NO3)3 □9H2O). Scanning Elec-tron Microscop y (SEM), Energy Dispe rsive Spectroscopy (EDS), X-ray Diff-raction (XRD) and M agic Angle Spinning/Nuclear Magnetic Resonance (MAS/NMR ) were employed for th e structural and molecular analysis of the solidified/stabilized samples. The unconfined compressive strength (UCS) and the leach-ability by the Toxicity Ch aracteristics Leaching Procedure (TCLP) of thesolidified/stabilized samples we re measured. Three major S/S processes wereemployed in this study and some sig nificant results are summarized as follows: I、Solidification/stabilization o f chromium-containing sludge with cementand cement /unsaturated polyester comp osite.1. All the solidified samples prepared with cement had compressive stren gth higher than 10 Kg/cm2 and leachability values which met the Taiwan EPA re- quirements for landfilldisposal. Nevertheless, they need to be disposed in se gregated landfill.2. Most of the solidified samples prepared with cement/unsat urated polyester composite had compressive strength higher than 150 Kg/cm2and leachability values which met the Taiwan EPA requirements for recycle-reuse re gulation.3. The samples prepared with cement exhibited loose structures,while thosewith cement/unsaturated polyester composite exhibited denser structures i n SEM observations.II、Solidification/stabilization of Cr2O3 or Cr(NO3)3 □9H2 O with cement and cement/unsaturated polyester composite. 1. Crystalline CaCr O4 was formed during the S/S of Cr2O3 with cement.This isattributed to the sub stitution of chromium for silicon in hydrated cementproducts.2. The degree of cement hydration decreased during the S/S of Cr(NO3)3 □9H2O with cement, an d it decreased more dramatically during the S/S of Cr(NO3)3 □9H2O with cement /unsaturated polyester composite ; indicating that chromium nitrate an d un saturated polyester could retard the extent of cement hydration.III、 Solidification/stabilization of Cr(NO3)3 □9H2O with cement constituents(i.e. (-C2S, C3S, and C3A).1. Formation of (-calcium chromium oxide hydrate ((-CaCrO 4 □2H2O) during the solidification/stabilization of chromium nitrate (Cr(NO3) 3 □9H2O) with (-C2S indicates the probable replacement of silicon by chromium in the calcium sili-cate hydrate (C-S-H). 2. Formation of calcium chromium si licate (CaCrSi4O10),calcium chromium oxide hydrate (CaCrO4 □2H2O), and calciu m dichromate (CaCr2O7) during the solidifi-cation/stabilization of chromium ni trate (Cr(NO3)3 □9H2O) with C3S indicatesthe probable replacement of silicon by chromium in the calcium silicate hydrate(C-S-H).3. Formation of aluminum ch romium oxide hydroxide (Al2(OH)4CrO4) during thesolidification/stabilization o f chromium nitrate (Cr(NO3)3 □9H2O) with C3Aindicates the probable interactio n between Cr and Al.