Sumiko Sanuki

Reductive stripping of Fe(III)-loaded D2EHPA with the aqueous solutions containing sulfur dioxide

The stripping of Fe(III)-loaded D2EHPA, which is known to be difficult, was studied in the presence of SO2. The stripping reaction of Fe(III) was greatly accelerated by the presence of SO2, generating Fe(II) as a stripped species. In the presence of SO2, the stripping of Fe(III) was favorable with all acids studied, including HC1, HC1O4, and H2SO4, and even with water. Among various factors, the partial pressure of SO2 was found to be the most important factor in controlling the rate of stripping as well as the rate of reduction of stripped Fe(III) in the aqueous phase. The removal of SO2 dissolved in an organic phase was easily done by washing with aqueous H2O2 solution.

Extraction of Ag(I) from aqueous thiocyanate solution with Primene JMT or TOA

Abstract Using Primene JMT or TOA, the extraction of thiocyanic acid and of Ag(I) thiocyanato-complex from aqueous thiocyanate solution was studied. On extraction of thiocyanic acid using aqueous phase containing 1.0 M NH4SCN and an organic phase containing 100–300 kg m−3 Primene JMT or TOA, (RNH3+·SCN−)o and (R3NH+·SCN−)o were formed with apparent equilibrium constants, log Kex,a, of 8.7 and 6.5, respectively. The extraction of 1×10−3 M Ag(I) from aqueous ammonium thiocyanate solutions by the thiocyanate salts of Primene JMT or TOA at concentrations ranging from 100 to 300 kg·m−3, and in the presence of ammonium thiocyanate at concentrations of 0.5–3.0 M can be summarized as follows: 2( RNH 3 + · SCN − ) o + Ag ( SCN ) 3 2− = K ex,3 (( RNH 3 + ) 2 · Ag ( SCN ) 3 2− ) o +2 SCN − , logK ex,3 =1.6 2( R 3 NH + · SCN − ) o + Ag ( SCN ) 3 2− = K ex,3 (( R 3 NH + ) 2 · Ag ( SCN ) 3 2− ) o +2 SCN − , logK ex,3 =2.5.

Stripping of silver from Primene JMT loaded with silver thiocyanate complexes

Abstract Stripping of silver from Primene JMT loaded with silver thiocyanate complexes was investigated, utilizing hydrolysis, anion exchange and reduction stripping reactions. The findings obtained are summarized as follows. (1) Precipitation stripping of AgSCN was almost impossible when water, aqueous NH 3 or NaOH was used as stripping solution. (2) Stripping or precipitation stripping reactions did not proceed quantitatively when HClO 4 or NaClO 4 , whose affinity for amine is strong, was used as stripping solution. (3) When NH 3 or NaOH solution containing NaBH 4 was used, reduction stripping proceeded producing aggregates of fine metallic Ag powder. (4) For efficient reduction stripping of Ag using a solution containing NaBH 4 , the addition of NH 3 or NaOH, and the use of NaBH 4 at more than twice the amount of Ag(I) in the organic phase, are required. (5) When Ag(I) extraction was done using Primene JMT that had been converted to the thiocyanate salt, the reduction efficiency deteriorated.

Precipitation stripping of Nd(III) carbonate from Nd(III)-loaded D2EHPA with NH3–(NH4)2CO3 solution

Abstract Precipitation stripping of Nd(III) carbonate from Nd(III)-loaded D2EHPA was investigated using a mixture of NH3 and (NH4)2CO3 as a stripping solution. Precipitation stripping of Nd(III) was achieved with appropriate NH3 and (NH4)2CO3 concentrations, however, it is necessary to make the concentration of NH3 greater than that of D2EHPA, and to keep the (NH4)2CO3 concentration above 0.3 kmol m−3. Increase in NH3 and (NH4)2CO3, over a concentration range suitable to recover Nd(III) carbonate, results in an increase in soluble Nd(III) in the aqueous phase, and thus a decrease in percent stripping. The precipitates produced in the aqueous phase were identified as Nd2(CO3)3·8H2O from the Nd(III) content, IR spectra, X-ray diffraction pattern, and thermal analyses. By calcining the precipitates at 873 and 973 K, cubic Nd2O3 and a mixture of cubic and hexagonal Nd2O3, respectively, was produced. The distribution of D2EHPA in an aqueous phase of high alkalinity was extremely limited. The ammonium salt of D2EHPA was formed by contact of D2EHPA in the organic phase with the aqueous phase of high alkalinity, resulting in a shift in the distribution equilibrium of Nd(III). Thus, Nd(III) is stripped into the aqueous phase and reacts with (NH4)2CO3 in stripping solution to form Nd(III) carbonate.

Decomposition of Tartarate during The Photocatalytic Reduction of Cu(II)-Tartarate Complex Solution

Decomposition of tartarate during the photocatalytic reduction of Cu()tartarate complex alkaline solution whose pH was adjusted with NaOH was studied using TiO2 powders. The effects of various factors, such as concentrations of NaOH and potassium sodium tartarate, intensity of UV irradiation and identity of TiO2 powders, were investigated on decomposition rate of tartarate. The main findings obtained are as follows: In the concentration range of 0.1~0.3 kmol・m-3 NaOH, both Cu() reduction and tartarate decomposition rates tend to linearly increase with the increase in NaOH concentration. As far as the same TiO2 catalyst was used, the adsorption amount of free tartarate ion as well as Cu()tartarate complexes ions onto TiO2 catalyst increase with the increase in NaOH concentration, indicating that adsorption of these ions directly concerns to the photocatalytic reaction. The amount of tartarate decomposition was around 10 of Cu() reduction. We detected CO 3 ions as the decomposed product, indicating a photocatalytic oxidation route of tartarate decomposition. Although the reduction rate of Cu() greatly decreased with the decrease in tartarare concentration, initial decomposition rates of tartarate were almost same despite of initial tartarate concentration. However, tartarate decomposition rates sharply increase near the termination of Cu() reduction reaction, showing more effective increase with the increase in initial tartarate concentration. By using different TiO2 catalysts, the amount of tartarate onto catalyst were affected by both surface area and adsorption activity of catalyst used. However, tartarate decomposition rate was not directly affected by the amount of tartarate adsorption in this case.