Extraction Of Chromium (iii) And Its Alkali Stripping Test Research

Chromium and it's compounds are widely used in the chemical industry, refractory material, metal materials and other fileds, and also they are the essential materials of aviation, aerospace, automobile, shipbuilding and defense-industry. But chromium is a toxic element and it can cause cancer to the human. So it is very important to research how to recycle the chromium-contained wastewater, waste residue and sludge. According to the rules of chromium ions in different pH environments, kinetics and technology of back-extraction with alkali were researched.1. Studying on extraction and separation of Cr-Ni mixture. The factors such as extractant concentration, saponification rate,extraction time, amount of 1-octanol were discussed. The results indicated that while 10% P204, 10% 1-alcohols and 80% kerosene, 30% saponification rate, organics volume/water volume 1, room temperature, extraction time 5 minutes, Cr-Ni separation coefficients reached 5.65; while 10% P507, 10% 1-alcohols and 80% kerosene, 30% saponification rate, organics volume/water volume 1, room temperature,extraction time 10 minutes, Cr-Ni separation coefficients reached 5.38.2. Studying on back-extraction of organic phase loaded chromium with alkali. The results indicated that while P204 loaded chromium, room temperature, organics volume/water volume 1, back-extraction time 10 minutes, back-extracted four times with 0.5mol/L NaOH, the back-extracting efficiency could reach 98.3%; while P507 loaded chromium, room temperature organics volume/water volume 1, back-extraction time 20 minutes, back-extracted four times with 2mol/L NaOH, the back-extracting efficiency could reach 98.8%.3. Studying on kinetics of back-extraction with alkali. The reaction order, the rate constants, the reaction rate equation and the activation energy were obtained. When P204 loaded chromium, the back-extraction rate equation is established as: v= Kf [Cr³⁺]_(o)^0.62[OH]^-0.24Kb[Cr³⁺]_(o)^-2.63[OH]^1.35, the activation energy is -57.46J/mol. When P507 loaded chromium, the back-extraction rate equation is established as: v = Kf [Cr³⁺]_(o)^0.06[OH]^0.25Kb[Cr³⁺]_(o)^-0.81[OH]^-0.02, the activation energy is -18.63J/mol.The main irnnovative is using alkali as back-extractant. It is easy to back-extract by alkali, while it's difficult to back-extract with high acid completely.