Lithium phosphate precipitation

H. N. Stokes prepared lithium monamidophosphate, as a crystalline powder, by precipitation from a soln. of the potassium salt on the addition of a lithium salt. When boiled with water, it furnishes lithium phosphate. He also made sodium monamidophosphate, (NH2)PO(ONa)2, by the action of sodium hydroxide on vol. vrn. 2 z... 

Sodium phosphate solution partial precipitation of lithium phosphate, Li3P04, in neutral solutions the precipitate is more readily obtained from dilute solutions on boiling. Precipitation is almost complete in the presence of sodium hydroxide solution. The precipitate is more soluble in ammonium chloride solution than in water (distinction from magnesium). 

In Mayer s1 method the lithium is precipitated and weighed as phosphate, excess of sodium hydroxide being added to cause complete precipitation but the process is condemned by Rammelsbcrg on account of the difficulty of eliminating the sodium. Carnot2 separates the lithium as fluoride, and transforms it into the sulphate. 

Extraction of HemiceUuloses from Various Pulps. The extraction procedure followed was that of Giertz and McPherson (6). Fifteen grams of unaged pulps [four kinds in all bleached kraft pulp (BP), unbleached kraft pulp (UBP), unbleached groundwood pulp (GP), and chlorited UBP] was treated with 290 mL of 10.9 lithium hydroxide solution for 1 h at room temperature and was stirred intermittently (see Table I for the characteristics of the pulps). After the samples were diluted to about 1 L, the insoluble material was filtered off. The extract (filtrate) was neutralized to pH 6 with 2 M phosphoric acid (300 mL) and was allowed to stand overnight. The precipitated lithium phosphate and /3-cellulose were separated by filtration. The filtrate was then concentrated to about 175 mL under reduced pressure at 30-40 °C. Salts present in the system were further precipitated with methanol and separated by filtration. The filtrate was again concentrated to about 60 mL. The filter paper was immersed into this concentrate to saturate the test sheets. 

Amorphous aluminum oxide has recently been proved to extract lithium from brines and bitterns having lithium concentrations of 0.83 and 13.1 mg/1, respectively. The sorption may be explained by the formation of hydrous lithium aluminum oxide. The sorption capacity of amorphous hydrous aluminum oxide was found to be 4.0 mmol/g. For brines and bitterns the lithium concentration factors on the sorbent attained values of 370 and 130, respectively equilibrium was reached after 7 days. The desorption of lithium ions was carried out with boiling water yielding a maximum concentration factor of lithium in the eluate of 46 in reference to the initial lithium concentration of the brines. Lithium was separated from the eluates by solvent extraction with cyclohexane containing thenoyltrifluoracetone and trioctyl-phosphine oxide, subsequent back extraction with hydrochloric acid, and precipitation of lithium phosphate by addition of K3P04. The purity of the precipitate amounted to at least 95% I7 21). 

Because of precipitating lithium phosphates during the course of the reaction the mixture forms a sticky slurry and so the use of a large stirring bar is recommended. 

Phosphorus species. Soluble phosphates precipitate lithium phosphate, more soluble in NH4CI than in H2O alone (distinction from Mg ). In dilute solutions the phosphate is not precipitated until the solution is boiled. The sensitivity of the test is increased by adding NaOH, forming a double phosphate of Na and Li. The phosphate dissolved in HCl is not at once reprecipitated on neutrahzation with NH3 (distinction from at least Ca " through Ra ty. Ethanol promotes precipitation. 

Precipitating lithium from low-lithium brines with sodium phosphate has also been tested, after the model of licons being precipitated from Searles Lake brine. Tandy and Canfy (1993) smdied the precipitation of lithium phosphate from Dead Sea potash pond end-liquor, and found that perhaps a 70% Li recovery could be obtained. By adding over a 30-fold molar excess of disodium phosphate to the lithium in the brine, adjusting the pH to 6-7, heating to 80°C, and with a 20-30 min residence time about 76% of the lithium would be precipitated along with dicalcium phosphate and the excess disodium phosphate. The precipitate contained about 0.3% Li, and could be leached with water to recover over 90% of the Li, with the remainder being in the residual phosphate precipitate. The filtrate contained about 1440 ppm Li in a sodium phosphate-chloride solution (Table 1.34). 

Alkaline hydrolysis with barium, sodium, or lithium hydroxides (0.2-4 M) at 110°C for 18-70 h126-291 requires special reaction vessels and handling. Reaction mixtures are neutralized after hydrolysis and barium ions have to be removed by precipitation as their carbonate or sulfate salts prior to analysis which leads to loss of hydrolysate. Correspondingly, peptide contents are difficult to perform by this procedure. Preferred conditions for alkaline hydrolysis are 4M LiOH at 145 °C for 4-8 h where >95% of tryptophan is recovered 291 An additional inconvenience of the alkaline hydrolysis procedure is the dilution effect in the neutralization step and thus the difficult application to the analyzer if micro-scale analysis is to be performed. The main advantage is the good recovery of tryptophan and of acid-labile amino acid derivatives such as tyrosine-0-sulfate1261 (Section 6.6) as well as partial recovery of phosphoamino acids, particularly of threonine- and tyrosine-O-phosphate (Section 6.5). 

Separation. In order to separate lithium from the other alkali metals, they are all converted into the chlorides (by evaporation with concentrated hydrochloric acid, if necessary), evaporated to dryness, and the residue extracted with absolute alcohol which dissolves the lithium chloride only. Better solvents are dry dioxan (diethylene dioxide, C4H802) and dry acetone. Upon evaporation of the extract, the residue of lithium chloride is (a) subjected to the flame test, and (b) precipitated as the phosphate after dissolution in water and adding sodium hydroxide solution. 

The flame coloration and the spectrum (p. 54) afford delicate tests for the presence of lithium. From solutions which are not too dilute it can be precipitated as phosphate, fluoride, or carbonate. Like sodium, it yields an antimonate of slight solubility, but in contradistinction to potassium its platino-chloride and hydrogen tartrate are soluble. 

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