CN1155528A

CN1155528A - Preparation of potassium-magnesium alum

Info

Publication number: CN1155528A
Application number: CN 96110247
Authority: CN
Inventors: 刘廷仰; 蒋乃燮
Original assignee: Nankai University
Current assignee: Nankai University
Priority date: 1996-07-11
Filing date: 1996-07-11
Publication date: 1997-07-30

Abstract

A process for preparing K-Mg-V mixed fertilizer features that the potassium hydrogen sulfate which is intermediate during covnentional production of potassium sulfate directly reacts on magnesium oxide in solid or liquid phase. Its advantages include simple production technology, low requirement on reaction condition, and low cost.

Description

Process for preparing potassium-magnesium alum

The invention relates to a preparation method of a potassium fertilizer and magnesium fertilizer mixed fertilizer. Kainite (i.e. K)₂SO₄With MgSO₄The composition) is an important agricultural compound fertilizer. Currently, there are two main approaches to preparing kainite: the method comprises the steps of evaporating natural mineral products or salt lake resources such as salt lake brine of Qinghai sulfate type introduced in CN1014818B and CN 1038252B to obtain potassium-magnesium mixed salt; CN1038799B describes a method for preparing picromerite by mixing carnallite, potassium chloride and mirabilite and carrying out solid-phase reaction. The quantity of natural mineral products or salt lake resources in China is limited, and the potassium-magnesium alum is prepared by taking the natural mineral products or salt lake resources as raw materials, most processes are complex, the production period is long, the product quality is influenced by factors of natural conditions, the control is not easy, and the market requirements can not be met. The other is the synthesis method which takes potassium chloride and concentrated sulfuric acid as raw materials to prepare potassium sulfate, takes magnesium oxide and sulfuric acid as raw materials to prepare magnesium sulfate, and then mixes the potassium sulfate and the magnesium sulfate according to a certain proportion to prepare the potassium-magnesium alum. Because potassium salt resources are deficient in China and potassium sulfate or kainite directly imported is expensive, potassium chloride is mainly imported as a raw material, potassium sulfate is prepared by a synthesis method and then is mixed with magnesium sulfate to prepare the kainite mixed fertilizer.

The preparation of potassium sulfate from potassium chloride includes the following two-step reaction process:

(1)

(2) (1) the step is an exothermic reaction, so that the method can be automatically carried out, the condition requirement is low, and the reaction is completely carried out. (2) The reaction reversibility is large, the forward smooth proceeding is not easy, special reaction conditions are needed, and the method is a main reason for high production cost of potassium sulfate.

The invention aims to provide a novel method for preparing kainite by directly reacting intermediate potassium bisulfate and magnesium oxide in the process of producing potassium sulfate by using a synthesis method.

The task of the invention is realized by the following technical scheme: adding sulfuric acid with concentration of 75-98% and potassium chloride solid with KCl content above 90% or its solution into a reactor with reflux device, wherein H₂SO₄Heating the reactor to 40-150 ℃ to react for 1-6 hours, cooling the product to 40-5 ℃ to separate out potassium bisulfate crystals, and returning the mother liquor after filtration and separation for use, wherein the weight ratio of KCl is 1: 0.5-1.5. Separating potassium bisulfate crystal with KHSO₄Mixing and grinding magnesium oxide solids with the acid equivalent of 0.25-0.5 time and the MgO content of more than 85%, carrying out solid-phase reaction at the temperature of 20-120 ℃ to obtain the kainite product, or preparing a solution with the concentration of 30-80% from the obtained potassium bisulfate crystals at the temperature of 90-120 ℃ to carry out liquid-phase reaction with the magnesium oxide for 0.5-1 hour, then filtering, and drying the precipitated solids to obtain the kainite product.

When the amounts of sulfuric acid and potassium chloride used are equivalent, the composition of the final kainite product is K₂SO₄·MgSO₄。

When the amount of sulfuric acid used exceeds the equivalent amount of potassium chloride, the amount of sulfuric acid used is excessive for the next reactionThe equivalent weight of the magnesium oxide used in the process, and the composition of the finally prepared potassium-magnesium alum product is K₂SO₄·2MgSO₄。

Compared with the prior art, the invention has the advantages that: the invention only needs to utilize concentrated sulfuric acid and potassium chloride in the conventional method to prepare the first step of the two-step reaction of potassium sulfate:

because the reaction can be automatically carried out, the generated hydrogen chloride can be quantitatively recycled, the HCl content in the recycled hydrochloric acid can reach 42 percent, the purity is high, and the method is suitable for hydrochloric acid products of various grades. Since potassium bisulfate is acidic, it can be mixed with magnesium oxide, which is basic, to react as follows:

or in the presence of an excess of sulfuric acid, the following reaction occurs:

the two reactions can be automatically neutralized, so that the process flow for preparing the kainite is greatly simplified, the requirements on reaction conditions are reduced, and the production cost is reduced.

Currently commercially available K₂SO₄·MgSO₄K produced according to the method with a price of 1400 yuan/ton₂SO₄·MgSO₄The price is 625 yuan/ton, so that obvious economic benefit is obtained.

The quality of the kainite product depends on the quality of the raw materials potassium chloride and magnesium oxide. When the KCl content in the used raw material potassium chloride is more than 90 percent and the MgO content in the magnesium oxide is more than 85 percent, the quality of the kainite prepared by the method reaches the national standard. The method can also prepare more refined kainite.

Example 1A reactor equipped with a reflux unit and a gas absorption unit was charged with 150 parts by weight of potassium chloride containing KCl 95% or more and 100 parts by weight of water, heated to 40 to 120 ℃ to partially dissolvethe potassium chloride, and 300 parts by weight of 98% concentrated sulfuric acid was added dropwise at such a rate that the generated hydrogen chloride gas was uniformly releasedAnd the pot is not too hot. The hydrogen chloride gas is absorbed by the gas absorption device. After the concentrated sulfuric acid is added dropwise, heating and reacting are continuously carried out for 2 hours, so that hydrogen chloride gas escapes completely, and 55 parts of hydrochloric acid with the HCl content of 41% is finally obtained. Then cooling the reaction solution to 20 ℃ to separate out potassium bisulfate crystals, and removing acid liquor attached to the crystals through filtration and centrifugation to obtain 250 parts of potassium bisulfate crystals. Taking 126 parts of potassium bisulfate prepared by the method and 29 parts of magnesium oxide with the MgO content of 95%, adding the mixture into a mixed liquid of 114 parts of mother liquor (which can be recycled) obtained by filtering and 108 parts of water, heating to 110 ℃, reacting for 0.5-1 hour, naturally cooling to 90 ℃, filtering out a solid product when the solid product is hot, and drying to obtain kainite K₂SO₄·MgSO₄104 parts of (1) and the content and the quality of the (104) meet the national standard (see example 2).

Example 2 Potassium hydrogen sulfate 230 parts, prepared by the method of example 1, and MgO content 85% were takenMixing the above solid with 50 parts of magnesium oxide, grinding, sieving with 40 mesh sieve, and oven drying at 120 deg.C for 4 hr to obtain Kalium-Mg-alum K₂SO₄·MgSO₄277 parts of a product. The result of sampling analysis was K₂33.02 percent of O, 12.62 percent of MgO, 19.17 percent of S and 5.6 percent of water-insoluble substances, and meet the national standard.

Example 3 the reaction apparatus and procedure were the same as in example 1 except that150 parts of potassium chloride containing 95% KCl, 400 parts of concentrated sulfuric acid (98%), and 40 parts of magnesium oxide containing 95% MgO were added in portions to adjust the pH of the reaction mixture to 7. Crushing and drying the obtained solid to obtain the kainite K₂SO₄·2MgSO₄510 portions, and the results of sampling analysis accord with the national standard.

Claims

1. A preparation method of kainite is characterized in that sulfuric acid with the concentration of 75-98% and potassium chloride solid with the KCl content of more than 90% or a solution thereof are added into a reactor with a reflux device, wherein H is₂SO₄KCl is 1: 0.5-1.5 (weight ratio), the reactor is heated to 40-150 ℃, the reaction is carried out for 1-6 hours, and then the reaction is cooledCooling the resultant to 40-5 deg.C to separate out potassium bisulfate crystals, filtering, separating, and returning the mother liquid to use, wherein the separated potassium bisulfate crystals and the KHSO are used₄Mixing and grinding magnesium oxide solids with the acid equivalent of 0.25-0.5 times and the MgO content of more than 85%, carrying out solid-phase reaction at the temperature of 20-120 ℃ to obtain the kainite product, or preparing a solution with the concentration of 30-80% from the obtained potassium bisulfate crystals at the temperature of 90-120 ℃ to carry out liquid-phase reaction with the magnesium oxide for 0.5-1 hour, and then filtering and drying the precipitated solids to obtain the kainite product.

2. Process for the preparation of leonite, according to claim 1, wherein the composition of leonite finally obtained is K, when the amounts of sulphuric acid and potassium chloride used are equivalent₂SO₄·MgSO₄。

3. Process for the preparation of leonite, according to claim 1, wherein when the amount of sulphuric acid used exceeds the equivalent amount of potassium chloride, the excess amount of sulphuric acid being the equivalent amount of magnesium oxide used in the next reaction, the resulting leonite having the composition K₂SO₄·2MgSO₄。