以微波水熱礦化法處理水中高濃度硼之研究

Abstract

硼化合物廣泛應用於陶瓷器皿、玻璃製品及液晶面版(LCD)製程中，同時亦排放高濃度之含硼工業廢水。根據相關文獻指出，硼為作物與人體之所需微量元素，然而過量硼對於動植物皆有一定毒害，因此各國亦限制排放廢水之硼濃度，其中台灣之放流水標準即要求水中硼濃度應小於1 mg/L，相對其他國家之標準較嚴格許多。因此，為因應高濃度含硼廢水處理以達嚴苛放流標準之迫切問題，本研究即針對此高濃度含硼水進行處理方法之發展。研究中主要由微波水熱礦化法為主軸，而三種不同藥劑添加方式為支架，以構成整體研究架構。 於微波液相硼回收實驗中，利用礦化作用產生結晶沈澱以回收水中硼，且於不同添加條件下皆具高處理效率。在單純添加氫氧化鈣條件下(Ca(OH)2 alone)，反應10分鐘後達90%回收效率，且反應後沈澱物於XRD分析中，觀察到偏硼酸鈣結晶之衍射峰。於氫氧化鈣與磷酸添加條件下(P addition)，於10分鐘內達99%處理效率，並可於沈澱物之XRD分析結果辨別出數種磷酸鈣結晶物。此外，分別測試三種預處理貝殼應用於此硼回收方法，實驗結果顯示，預處理牡蠣殼之硼處理效率為最佳，可於10分鐘內達到95%，而於預處理文蛤與蜆殼條件下，與單純添加氫氧化鈣條件相似，僅達到90%之硼處理效率。而在貝殼預處理實驗中，利用複合微波加熱方式轉化生物貝殼材料，並探討不同材質作為微波吸收介質之技術可行性。實驗結果顯示，相較於其他三種微波吸收材料，氧化銅具有較快之升溫速度。而搭配二氧化鋯使用時，於CuO:ZrO2 = 1: 1之比例及600W微波功率20分鐘下，除可降低此複合微波介質之碎裂情形，可轉換大部分碳酸鈣為氧化鈣，以供硼處理所需添加藥劑使用。 根據本研究結果，複合微波於貝殼之前處理為可行之技術，然而拓展至實際應用尺寸仍須加以修正與改進。而無論於使用商用藥劑之添加條件下，抑或於預處理貝殼添加條件下，水中硼回收皆具有90%以上之回收效率。而此方法於應用時，亦需考慮水體之酸鹼值、硼初始濃度以及其他干擾物質之量以做出適當調整，並達最佳硼回收效果。

Boron compounds are widely-used raw materials in industries, such as ceramic, glass and liquid crystal display (LCD) process. Wastewaters from these processes often contain elevated boron concentrations, and it in aqueous systems may be harmful to human and plants. In this study, boron recovery, calcium hydroxide (Ca(OH)2 alone), Ca(OH)2 with phosphoric acid (H3PO4) addition (P addition) and pretreated shells were used to remove and recover boron from water using hydrothermal methods. For the case of Ca(OH)2 alone and MW(Microwave) hydrothermal method, experimental results showed that boron recovery efficiency achieved 90% within 10 min, and crystals of Ca2B2O5•H2O were found in the precipitates as indicated by the XRD analysis. For the case of P addition and the MW hydrothermal method, boron recovery efficiency reached 99% within 10 min, and calcium phosphate species (CaHPO4．H2O, CaHPO4 and Ca10(PO4)6(OH)2) were formed. For the case of pretreated shell, three types of crushed shells (oyster, hard clam and freshwater clam) were pretreated and then reused as mineralizers to remove and recover the boron from concentrated wastewater by using the MW hydrothermal method. The oyster shells pretreated by heat performed better than heated hard clam and freshwater clam shells, and the boron recovery efficiency reached around 95% within 10 min of reaction time. In order to use bio-shell as substitute of calcium hydroxide, shell pre-treated method was also considered in this study. Oyster shells were transformed by hybrid microwave heating method, and the effect of different microwave absorption materials were also investigated. Comparing with three other microwave absorption materials, CuO performed a rapider rate of heating. The temperature of CuO reached 950 oC after 3 min, and CuO-ZrO2 (1:1) microwave absorbent might have less degree of disruption. In addition, oyster shells were almost decomposed and became CaO with CuO-ZrO2 (1:1) microwave absorbent at power of 600W after 20 min of reaction time. According to the experimental results, pretreatment of shells by composite microwave heating is a feasible method. However, some modifications and improvements should be done for practical use. In addition, an effective method for boron recovery by microwave with commercial reagents or pretreated shells was found. There are several factors that should be considered, such as pH value, initial boron concentration and interference compound before adopting this method.