Recovery of nitric acid from waste etching solution using solvent extraction.
A process was developed to recover nitric acid from the waste stream of wafer industry using solvent extraction technique. Tributyl phosphate (TBP) was selected among several extractants because of its better selectivity towards HNO(3), overall superiority in operation, favorable physical properties and economics. The waste solution containing 260 g/L CH(3)COOH, 460 g/L HNO(3), 113 g/L HF and 19.6g/L Si was used as feed solution for process optimization. In the pre-treatment stage >99% silicon and hydrofluoric acid was precipitated out as Na(2)SiF(6). Equilibrium conditions for HNO(3) recovery were optimized from the batch test results as: four stages of extraction at an organic:aqueous (O:A) ratio of 3, four stages of scrubbing at O:A ratio of 5 and five stages of stripping at an O:A ratio of 1.5. The extraction of HNO(3) was suppressed by the presence of acetic acid (HAc) in the feed solution. To examine the feasibility of the extraction system a continuous operation was carried out for 200 h using a multistage mixer-settler. The concentration of pure HNO(3) recovered was 235 g/L with a purity of 99.8%.
Separation and Recovery of Acid from Waste Acid Mixture in Silicon Wafer Manufacturing Industry.
シリコンウエハーエッチング工程廃液に溶媒抽出法を適用して，酸を分離・回収するために基礎研究を行った．抽出剤に2-エチルヘキシルアルコール（EHA）とリン酸トリブチル（TBP）を用いて，酢酸，硝酸，フッ酸およびシリコンの4成分を含む廃液から単一成分の酢酸，硝酸およびフッ酸の分離を検討した．EHAは酢酸に対する抽出選択性に優れていた．TBPは硝酸およびフッ酸の回収に有効であった．EHAを使用した場合，エッチング廃液から3段の向流抽出，10段の向流洗浄および水による4段の向流剥離（逆抽出）の操作によって2.0mol/dm3の酢酸が回収できる．TBPを使用した場合，3段の向流抽出，10段の向流洗浄，5段の向流剥離の操作によって6.0mol/dm3の硝酸が回収できる．TBPにより4段の向流抽出，9段の向流剥離によって6.0mol/dm3のフッ酸が回収できる．得られた基礎試験の結果から，シリコンウエハーのエッチング廃液からの酸回収のプロセスを構築した．
Interaction of Diclofop-Methyl and MCPA on Wild Oats (Avena fatua)
Diclofop-methyl {methyl 2-[4-(2,4-dichlorophenoxy)phenoxy] propanoate} loses part of its activity on wild oats (Avena fatua L.) when it is applied in combination with ester or amine formulations of MCPA {[4-chloro-o-tolyl)oxy] acetic acid.} Uptake of diclofop-methyl is reduced in the presence of commercial formulations of MCPA, particularly amine formulations, which are only partly compatible with the diclofop-methyl formulation. With added MCPA, regardless of formulation, hydrolysis of diclofop-methyl to the acid diclofop is slowed down, both in intact wild oat plants and in a crude leaf extract. At the same time, conversion of any acid formed to inactive conjugates is accelerated in the presence of MCPA. It is concluded that the loss of activity of diclofop-methyl by MCPA can be accounted for by the effects of MCPA on uptake and metabolic conversion of diclofop-methyl.