Spectrophotometric Determination of Uranium in the Presence of Alkaline Earths

A spectrophotometric method for the determination of uranium in the presence of an excess of alkaline earths was needed to perform investigations of the precipitation systems uranyl nitrate -sodium carbonate - alkaline earth chlorides

Precipitation and Hydrolysis of Uranium(VI) in Aqueous Solutions. III. Uranyl Nitrate - Sodium Carbonate - Strontium Chloride

In the precipitation system uranyl nitrate - sodium carbonate - strontium chloride the influence of changes in concentration of uranyl nitrate on the precipitation of uranium was studied. The »concentration maximum« was found to occur when the equivalent concentrations of the precipitating components are satisfying the following expressions: 1.5 1[U02(NOah] > 0.7 [U02(N03}2] - 1.36 (1) (2) The final pH values of the systems were about 6. It was shown that expression (1) is valid in the range of 1 X 10-1 N to 1 X 10-4 N of uranyl nitnte, while expression (2) is valid in the range of 1 X 10-1 N to 2 X 10-a N of uranyl nitrate. The coprecipitation of uranium with strontium carbonate exceeded 850/o when the following relations existed between the equivalent concentrations of the precipitating components: [SrCl2] >- [Na2C03] (3) 1[Na2COa] ~ 0.76 [U02(N03}2] + 0.7 (4) Expression (4) was found to be valid in the range of 6 X 10-2 N to 2 X 10-4 N of uranyl nitrate. The region where more than 850/o of uranium was coprecipitated was represented by means of a precipitation body in a coordination system of the concentrations of strontium chloride (x - axis), sodium carbonate (y - axis) and uranyl nitrate (z - axis)

Investigations of Complex Precipitation Systems

A survey of methods available for investigations of complex precipitation systems under dynamic conditions and under conditions of stable and metastable equilibrium is represented. Examples given pertain to the calcium and magnesium phosphate and calcium oxalate precipitation systems. Solubility curves as well as precipitation curves and diagrams yield information on the influence of reactant concentrations (and/or concentrations of other solution constituents) on the properties of precipitates. Characteristic parts of precipitation diagrams are the precipitation boundary (boundary between metastable and unstable solutions) and the boundary between the concentration regions within which heterogeneous and homogeneous nucleation respectively prevail. At equilibrium the precipitation boundary enables calculations of solubility and complex stability constants, otherwise it yields information on the kinetics of mononuclear crystal growth. From the heterogeneous/homogeneous nucleation boundary the critical supersaturation for homogeneous nucleation and the interfacial energy and critical radius of the respective homogeneous nucleus may be determined. Kinetic experiments give information on the rates and mechanisms of the rate determining precipitation processes involved. It has been shown that in the concentration region of heterogeneous nucleation crystal growth and subsequent (or simultaneous) aggregation are rate determinant, whereas in the homogeneous nucleation region aggregation of particles is dominant in all stages of precipitate formation and the formation of colloids (hydrophobic precipitates) and highly hydrated precursors (hydrophilic precipitates) may be expected. Examples of kinetic curves pertaining to the heterogeneous and homogeneous nucleation region respectively are presented

Precipitation and Hydrolysis of Uranium(VI) in Aqueous Solutions. II. Uranyl Nitrate - Sodium Carbonate - Alkaline Earth Chlorides

The precipitation systems: uranyl nitrate (2X IQ-3N) - sodium carbonate - Me chlorides (Me = Ba, Sr, Ca, Mg) were investigated and compared. The corresponding precipitation diagrams were constructed by plotting the percentage of uranium precipitated as a function of the concentrations of sodium carbonate and alkaline earth chloride. Solid phase formation starts in all systems at sodium carbonate concentration of 1.6.X 10-aN and pH"\u27 5, when a critical concentration of the particular alkaline earth chloride, necessary for precipitation, is exceeded. A precipitation maximum with more than 80% of uranium precipitated occurs at 3X 10-:w of sodium carbonate and pH ,.., 6. At high concentrations of both sodium carbonate and alkaline earth chloride uranium is coprecipitated with the corresponding alkaline earth carbonate. The coprecipitation regions are shifted to higher co·ncentrations of the precipitating components in the normal order of alkaline earth ions. A region with less than 15°/o of uranium precipitated separates the regions of precipitation and coprecipitation of uranium in the presence of strontium, calcium and magnesium chloride. With barium chloride in solution, this minimum is replaced by a »transitional« precipitation region with 55- 95% of uranium precipitated. When sodium carbonate is present in concentrations higher than the concentr11tions of alkaline earth chloride soluble complex, uranyl carbonates prevail in all systems

Kinetics of Precipitation and Cryst~l Growth of Dicalcium Phosphate Dihydrate

The kinetics of the precipitation and crystal growth of dicalcium phosphate dihydrate (DCPD) was followed in 0.15 M sodium chloride solutions at constant pH (pH = 5.0) and temperature (25o C). Precipitations were performed from equimolar solutions of calcium chloride and sodium phosphate prepared by direct mixing of the reactants. The amount of precipitate formed (X moles per 1) was calculated from the quantity of sodium hydroxide added by a pH-stat device. The system is of physiological interest, because precipitation of DCPD may play an important role during dental caries formatio

A coding problem for pairs of subsets

Let $X$ be an $n$--element finite set, $0<k\leq n/2$ an integer. Suppose that $\{A_1,A_2\}$ and $\{B_1,B_2\}$ are pairs of disjoint $k$-element subsets of $X$ (that is, $|A_1|=|A_2|=|B_1|=|B_2|=k$, $A_1\cap A_2=\emptyset$, $B_1\cap B_2=\emptyset$). Define the distance of these pairs by $d(\{A_1,A_2\} ,\{B_1,B_2\})=\min \{|A_1-B_1|+|A_2-B_2|, |A_1-B_2|+|A_2-B_1|\}$. This is the minimum number of elements of $A_1\cup A_2$ one has to move to obtain the other pair $\{B_1,B_2\}$. Let $C(n,k,d)$ be the maximum size of a family of pairs of disjoint subsets, such that the distance of any two pairs is at least $d$. Here we establish a conjecture of Brightwell and Katona concerning an asymptotic formula for $C(n,k,d)$ for $k,d$ are fixed and $n\to \infty$. Also, we find the exact value of $C(n,k,d)$ in an infinite number of cases, by using special difference sets of integers. Finally, the questions discussed above are put into a more general context and a number of coding theory type problems are proposed.Comment: 11 pages (minor changes, and new citations added

Application of Microdiffusion Methods for the Determination of Carbon Dioxide in Solid Carbonates

A new absorption device is recommended as a modification of the Cavett apparatus. Its application for the determination of carbon dioxide in solid carbonates is discussed. Barium carbonate has been used as a test substance. Determinations of carbon dioxide were carried out by decomposing the samples with hydrochlor ic acid, absorbing the evolved gas in bc:rium hydroxide solution and re-titrating the excess alkali with standard hydrochloric a cid solution to a thymolblue end-point. Carbon dioxide has been determined in the range of 0.3-3 mg. with relative standard errors of 18-2Q/o, respectively. Estimations have been made with quantities of carbon dioxide as low as 70 μg. The results of carbon dioxide determinations in a precipitate of the system uranyl nitrate - barium chloride - natrium carbonate - water are shown