The present invention discloses a preparation process of food-grade potassium dihydrogen phosphate, wherein phosphoric acid prepared from wet-process phosphoric acid is used for the preparation of high-purity potassium dihydrogen phosphate. The preparation process of food-grade potassium dihydrogen phosphate provided in the present invention effectively reduces the preparation cost of the high-purity potassium dihydrogen phosphate and has the advantage of high process controllability, and by such a process, high-purity potassium dihydrogen phosphate crystals that meet the food-grade requirements can be produced, which crystals have uniform particle size distribution and comprises few fine powder, having a very high market value.

A process is provided using a concentrated sodium bicarbonate solution as a solubilizer mixed with a calcium hydroxide to chemically produce an insoluble calcium carbonate and produce an alkaline liquid solution, then passing the alkaline liquid solution through detrimental gases in a scrubber to produce an enhanced sodium bicarbonate which regenerates the sodium bicarbonate thus creating a continuous closed loop. The process can also produce a sodium phosphate (trisodium phosphate) by mixing the alkaline liquid solution with a phosphoric acid.

A method for manufacturing a dense layer that includes: supplying a substrate and a suspension of non-agglomerated nanoparticles of a material P; depositing a layer on the substrate using the suspension; drying the layer thus obtained; and densifying the dried layer by mechanical compression and/or heat treatment. The method is characterised in that the suspension of non-agglomerated nanoparticles of material P includes nanoparticles of material P having a size distribution having a value of D50. The distribution includes nanoparticles of material P of a first size D1 between 20 nm and 50 nm, and nanoparticles of material P of a second size D2 characterised by the value D50 being at least five times less than that of D1, or the distribution has a mean size of nanoparticles of material P less than 50 nm, and a standard deviation to mean size ratio greater than 0.6.

Provided is a method for producing a high-purity aqueous lithium salt solution, the method allowing filtering aluminum phosphate in a short time. The method for producing a high-purity aqueous lithium salt solution includes: a step of adjusting the pH of a slurry containing a mixture of lithium phosphate and aluminum hydroxide obtained from a first aqueous lithium salt solution being a raw material to a range of 2 to 3 to obtain a precipitate of aluminum phosphate; a step of filtering off and removing the precipitate of aluminum phosphate to obtain a second aqueous lithium salt solution; and a step of purifying the second aqueous lithium salt solution to obtain a high-purity aqueous lithium salt solution.

A positive electrode active material including a nickel-containing lithium transition metal oxide containing nickel in an amount of 60 mol % or more based on a total number of moles of transition metals excluding lithium, and a coating layer which is formed on a surface of the nickel-containing lithium transition metal oxide and includes a lithium-containing inorganic compound, a nickel oxide, and a nickel oxyhydroxide is provided. A method of preparing the positive electrode active material, and a positive electrode for a lithium secondary battery and a lithium secondary battery which include the positive electrode active material are also provided.

The present invention discloses a preparation process of food-grade potassium dihydrogen phosphate, wherein phosphoric acid prepared from wet-process phosphoric acid is used for the preparation of high-purity potassium dihydrogen phosphate. The preparation process of food-grade potassium dihydrogen phosphate provided in the present invention effectively reduces the preparation cost of the high-purity potassium dihydrogen phosphate and has the advantage of high process controllability, and by such a process, high-purity potassium dihydrogen phosphate crystals that meet the food-grade requirements can be produced, which crystals have uniform particle size distribution and comprises few fine powder, having a very high market value.

The present invention relates to compounds and their nonlinear optical (NLO) crystals of A.sub.3B.sub.11P.sub.2O.sub.23 (A=K, Rb, Cs), their producing method and uses thereof. A.sub.3B.sub.11P.sub.2O.sub.23 (A=K, Rb, Cs) belong to triclinic crystal system, and have a space group of P1, crystal cell parameters of a=6.284(8)-8.784(3) , b=6.338(3)-8.838(3) , c=6.463(3)-8.963(3) , =70-105, =75-106, =76-107 and Z=1 and a unit cell volume of V=257.4(3)-696.0(6) .sup.3. A.sub.3B.sub.11P.sub.2O.sub.23 (A=K, Rb, Cs) compounds were prepared by a high-temperature solid-state reaction method or a hydrothermal method, and A.sub.3B.sub.11P.sub.2O.sub.23 (A=K, Rb, Cs) NLO crystals were prepared by a high-temperature solid-state reaction method, a hydrothermal method or a solution method. These materials can be used to manufacture second harmonic generator, up-down frequency converter, optical parametric oscillator, etc.

An embodiment of the present invention provides a method for preparing a solid lithium salt from a lithium solution including the steps of, preparing a mixture in which a phosphorus-containing material is added to a lithium solution in step 1; adding a basic solution to the prepared mixture to adjust the pH in step 2; making the pH-adjusted mixture react by raising its temperature and filtering to recover lithium phosphate in step 3; preparing an acid lithium solution in which distilled water and acid are added to the recovered lithium phosphate, in step 4; and recovering a solid lithium salt by evaporative concentration of the acid lithium solution, in step 5.

The present invention provides a method for the preparation of multi-nutrient potassic fertilizer, by recovering potassium from sugarcane molasses based alcohol distillery effluent (commonly known as spent wash). The process involves pre-treatment of spent wash to clarify the aqueous phase and utilization of the treated spent wash in production of potassic fertilizer. The present invention enables utilisation of spent wash for recovery of value-added product (viz., potash fertiliser of >99% purity) and improves ease of Zero Liquid Discharge compliance by subjecting the relatively benign process effluent to industrially practiced techniques for water recovery and salt reclamation.

A positive electrode active material including a nickel-containing lithium transition metal oxide containing nickel in an amount of 60 mol % or more based on a total number of moles of transition metals excluding lithium, and a coating layer which is formed on a surface of the nickel-containing lithium transition metal oxide and includes a lithium-containing inorganic compound, a nickel oxide, and a nickel oxyhydroxide is provided. A method of preparing the positive electrode active material, and a positive electrode for a lithium secondary battery and a lithium secondary battery which include the positive electrode active material are also provided.