CS242284B1 - A method for treating waste, calcium, sodium sludge - Google Patents

Abstract

The purpose of the solution was to find an industrially feasible method of processing lime soda sludge into fertilizer. This goal is achieved by reacting the thickened sludge, stripped of at least 50% of its original chloride content, with kieserite and possibly anhydrous potassium sulfate until the reaction mixture solidifies, which is then ground.

Description

The invention relates to a process for processing waste, calcium, sodium sludge into fertilizer.

In the production of soda by the Solvay process, about 10 to 12 m ^{3 of} waste liquor is removed per tonne of soda ash produced, which, at a density of 1100 to 1113 kg / m ^3, contains:

up to 95 kg / m ³ CaCl 2, up to 50 kg / m ³ NaCl, up to 15 kg / m ³ CaCO ³ , up to 5 kg / m ³ CaSCU, up to 4 kg / m ³ CaO.

In addition, the tailings from the lime extinguishing drums and the slag from the furnaces of the steam boilers, or even the technological ones.

These wastes are disposed of either jointly or separately by leaching into tanks where solid phase is collected. When the sodium sludge is thickened, the clarified salt solution is discharged into the watercourse and the concentrated solid phase with the heap is at the cost of adverse effects on the environment.

All attempts to use these thickened sludge in construction or agriculture have so far been unsuccessful. In addition to the residual chloride content, a high moisture content prevents the use, so that the physico-mechanical properties of these sludge are unfavorable for any handling.

The economic results of the proposed processes are more or less unfavorable precisely for the cost-intensive operations necessary to reduce both chloride and moisture content. For the same reasons, the method according to MS. No. 193,921, which is based on the reaction of sodium sludge with calcium oxide to form a powder.

The process of treating waste, calcium, sodium sludge into a fertilizer according to the invention seems to be more advantageous, characterized in that the concentrated sludge, free of at least 50% of the original chloride content, is reacted with kieserite or optionally with anhydrous alkali metal sulfate. , which is then pulverized. The amount of kieserite used is 5 to 50% by weight of the concentrated sludge, preferably 20 to 30%.

The anhydrous alkali metal sulfate may be potassium sulfate. The amount of potassium sulphate used corresponds to the molar ratio of MgSO4: K2SO4.

The process of utilization of the sodium sludge according to the invention can be counted among the processes economically resp. less energy intensive, since only the energy of physical and chemical reactions and those substances that are commonly used alone in this sector of the national economy are consumed to adjust the mechanical properties of sludge for use in agriculture.

In the mixture prepared according to the invention, the reactions take place:

Ca (OH) ₂ 4- MgSO 4. H 2 O + H 2 O = = Mg (OH) 2 + CaSO 4 .2H 2 O (1j,

MgSO4. H 2 O + (n - 1) H 2 O = MgSO 4.

. nH 2 O, (2) wherein n = 2, 4, 5, 6, 7.

Since the reaction (2) is slow, it is more useful for storing the calcium magnesium fertilizer thus prepared.

A modification of this process is based on the addition of anhydrous alkali metal sulphate such as potassium sulphate in addition to the above-mentioned kieserite (MgSO 4 .H 2 O 3).

MgSO4. H2O + K2SO4 + 5 H2O = K2SO4.

. β H2O (3j also reacts by conversion of gypsum:

CaSO4.2 H2O + K2SO4 + 2 H2O = K2SO4. CaSO4.4 H2O (4j but also:

2 (CaSO 2 · 2 H 2 O) + MgSO 4 + K 2 SO 4 = = 2 CaSO 4. MgSO4. K2SO4.2 H2O + 2H2O (5)

This treatment also has a favorable effect on the physical and mechanical properties of the product.

The amount of kieserite used is in the range of 5 to 50% by weight of the wet washed sludge used, potassium sulfate can be used up to the MgSCl ratio; K2SO4 to 1, preferably only up to the stoichiometric amount corresponding to the formation of the schonite mineral (K2SO4. CaSO4.6H2O).

The process according to the invention is also apparent from the following exemplary embodiment.

Exemplary embodiment

Raw concentrated sodium sludge obtained from a sedimentation tank of the following composition:

20.1% CaO tot., 8,0% CaO as Ca (OH) 2, 0.5% MgO, 1.4% On, 4.6% whose-, 11.1% CO3 ² -, 60.6% moisture,

was introduced into a stirred reactor where it was washed with 1.5 times the amount of water. The resulting suspension was dewatered on a filter press. The sludge thus washed contained:

34.7% CaO total,

21.5% CaO as Ca (OH) 2,

1.3% MgO,

0,3% Na,

1.4% Cl ^- ,

13.9% CO3 ² -,

40.0% humidity.

kg of the sludge thus washed was conveyed to a kneader, where the sludge was kneaded with 20 kg of kieserite. The obtained plastic mass was transported from the kneader to the warehouse, where it was left for 24 hours. After this time, the hardened material was extracted, comminuted and shipped as fertilizer. Fresh calcium-magnesium fertilizer had the following composition:

24.5% CaO tot., 15.0% CaO as Ca (OH) 2, 5.0% MgO, 0.6% On, 2.0% Cl ^- , 9.4% CO3 ^2- , 13.0% SO4 ² , 38.0% humidity.

If drying is prevented, the fertilizer can be stored without the risk of sagging and sintering.

Claims (2)

SUBJECT Process for treating waste, calcium, sodium sludge into fertilizer, characterized in that the concentrated sludge, free of at least 50% of the original chloride content, is reacted with kieserite, optionally with anhydrous alkali metal sulphate, until the reaction mixture solidifies, which is then ground, wherein the amount of kieser of the invention is here equal to 5 to 50% by weight of the concentrated sludge, preferably 20 to 30%, and the amount of alkali metal sulphate used corresponds to the molar ratio MgSO 2: K 2 SO 4 = 1. 2. The process of claim 1 wherein the anhydrous alkali metal sulfate is potassium sulfate.