兩段式奈米薄膜系統純化/濃縮電鍍製程含鉻廢液及質量傳輸之研究

Recovery of chromate from a spent plating solution by two stage nanofiltration process and mass transfer evaluation

莊珮綺(Pei-Chi Chuang)

指導教授 ： 陳孝行

國立臺北科技大學/工程學院/環境規劃與管理研究所/碩士(2006年)

https://doi.org/10.6841/NTUT.2006.00087

摘要

本研究利用鉻酸pKa之特性建立兩段式奈米薄膜，以純化、濃縮混合性金屬廢液中之鉻酸離子。由於電鍍廠鍍鉻廢液成分複雜，包含具高毒性之六價鉻及鎳（Ni2+）、銅（Cu2+）金屬離子(以大興鍍金公司為例)，為使其回收高純度鉻酸離子於製程中再利用，本研究利用奈米薄膜之特性；對二價離子具有良好的截流效率，再利用鉻酸中性pKa2＝6.5之特性；於酸性條件下（pH＜6.5）以一價離子(HCrO4-)型態存在，設置第一階段奈米薄膜；分離二價的鎳、銅離子與一價鉻酸離子；純化鉻酸離子，於鹼性條件下（pH＞6.5）以二價離子(CrO42-)型態存在，設置第二階段奈米薄膜；截留濃縮鉻酸離子。
本研究採連續式及批次式試驗，針對進流水pH值、操作壓力的控制及系統迴流體積比，探討奈米薄膜對實廠含鉻之電鍍廢液的分離機制及現象，並依據Spiegler, Kedem與Katchalsky (S.K.K)所提出的非均相熱力學傳輸模式(The non-equilibrium thermodynamic)推估計算反應參數；包括離子之截流係數σ及溶質滲透係數ω。
研究結果發現，當進流水pH值為3時；奈米薄膜對Ni2+截留率為94.0%、Cu2+為86%，HCrO4-為25%；可達到純化鉻酸離子之目的，因此可將第一階段奈米薄膜系統進流水pH值設定為3。當進流水pH值為10時；奈米薄膜對二價鉻酸離子的截流率可達99%，因此第二階段奈米薄膜系統進流水pH值設定為10。離子截留效率受到進流水總離子強度大小的影響，進流離子濃度越高，流通量越小；截留效果越差。此外；奈米薄膜對具相同電性的鎳（Ni2+）、銅（Cu2+）離子截留率取決於離子水合能的大小。依據S.K.K薄膜擴散傳輸模式計算得知，HCrO4-之截流係數σ=0.2725；CrO42-＝0.9961；Ni2+=0.7706；Cu2+=0.6003，表示離子截流係數σ取決於離子之價數、電性及水合能大小，而非分子量。

關鍵字

奈米薄膜 ； 鉻酸 ； 非均相熱力學傳輸模式 ； 水合能

並列摘要

A two-stage nanofiltration was proposed to purify and concentrate chromium (VI) from the spent plating solution with impurities such as copper and nickel ions present. For pH of lower than 6.5, chromium is considered as monovalent species HCrO4- but for pH higher than 6.5, chromium is considered as divalent species CrO42-. Nanofiltration is characterized as a retention of multivalent ions higher than monovalent ions, the pH in the first stage is lower than 6.5, NF is used to retain Cu2+ and Ni2+ in the concentrate stream, and separation of HCrO4-. In the second stage, the pH is higher than 6.5, NF can concentrate CrO42-.
A two-stage nanofiltration was studied with batch and continuous experiments to investigate the influence of pH, operating pressure, and system volume ratio. This approach is based on the phenomenological model of Spiegler, Kedem and Katchalsky, and then calculated the phenomenological parameters, the membrane reflection coefficient σ, and the solute permeability ω of four kinds of ions.
The results of this investigation implies that pH was 3, was obtained the Ni2+ retention rate of about 94 %, the Cu2+ retention rate of about 86 %, the HCrO4- retention rate of about 25%. Consequently, the pH value in the first stage can be determined as 3. While the pH value of feed water was 10, was obtained the CrO42- retention rate of about 99%. Therefore, the pH value in the second stage can be determined as 10. For higher concentrations (higher ionic strength) flux and retention decrease, the rejection of Ni2+ and Cu2+ depend on the hydration energy of ions. According to the S.K.K model, the membrane reflection coefficient σ for HCrO4- was determined as 0.2725, 0.9961 for CrO42-; 0.7706 for Ni2+, and 0.6003 for Cu2+. The σ values depend on the charge and hydration energy of ions instead of molecular weight.

並列關鍵字

Nanofiltration ； Chromium ； Non-thermodynamics ； Hydration energy

參考文獻

[1] C. Visvanathan, R. Ben Aim and S. Vigneswaran, "Application of cross-flow electro-microfiltration in chromium wastewater treatment," Desalination, vol.71, no.3, 1989, pp. 265-276.

[2] G.S. Gupta and Y.C. Sharma, "Environmental management of textile and metallic industrial effluents," Journal of Colloid and Interface Science, vol. 168, no. 1, 1994, pp. 118-124.

[3] J. Pradhan, S.N. Das and R.S. Thakur, "Adsorption of hexavalent chromium from aqueous solution by using activated red mud," Journal of Colloid and Interface Science, vol. 217, no. 1, 1999, pp. 137-141.

[6] P. Eriksson, "Nanofiltration extends the range of membrane filtration," Environmental Progress, vol. 7, no. 1, 1988, pp. 58-62.

[7] H.C. Van der Horst, Timmer J.M.K, T. Robbertsen and J. Leender, "Use of nanofiltration for concentration and demineralization in the dairy industry: Model for mass transport," Journal of Membrane Science, vol. 104, no. 3, 1995, pp. 205-218.