Method for the acid treatment of red mud

Abstract

The invention relates to the metallurgical industry, specifically to the acid treatment of red mud obtained in the process of producing alumina, and can be used in technologies for recycling waste from alumina refinery holding ponds. The method for the acid treatment of red mud involves leaching using a leaching agent comprised of water-soluable aliphatic carbonic acids having fewer than 3 carbon atoms per molecule, filtering the solution, and separating the recoverable end products. To ensure a high level of recovery of valuable components and the increased productivity of the process, leaching is conducted with the addition of red mud in portions and with the control of pH values, and when a target pH value of between 2.3 and 3.8 is reached, no more red mud is added, and once leaching is complete, the solution is kept at a given leaching temperature for no less than one hour.

Claims

1. A method for the acid treatment of red mud comprising: a. leaching red mud in a solution using a water-soluble aliphatic carboxylic acid having fewer than 3 carbon atoms as a leaching agent, wherein the leaching is carried out with red mud being added in small portions with continuous pH monitoring, wherein the addition of red mud is terminated when a predetermined solution acidity of pH of 2.3-3.8 is reached, and the solution is kept at a constant leaching temperature for at least one hour after the last portion of the mud is added; b. filtering the solution from step a. and separating recoverable end products.

Description

(1) The object of the invention is to optimize the conditions for leaching red mud with acids during mud processing.

(2) The technical result is to provide a high degree of valuable component recovery and to increase the productivity of the process.

(3) The above technical result is achieved in that in a method for the acid treatment of red mud comprising leaching using as the leaching agent water-soluble aliphatic carboxylic acids with fewer than 3 carbon atoms in the molecule, filtering the solution, and separating the recoverable end products, the leaching is carried out with the batch addition of red mud with pH control, when the target pH of 2.3-3.8 is reached, stopping the addition of red mud, and upon completion of the leaching, keeping the solution at a given leaching temperature for at least one hour.

(4) The acid treatment of red mud with maximum recovery of valuable components, a high process productivity, and an efficient separation of the resulting suspension into solid and liquid phases is achieved by controlling the pH, conducting the leaching at a given pH of 2.3-3.8, and keeping the solution at the given leaching temperature upon its completion.

(5) The pH value of 2.3-3.8 is determined based on the concurrent provision of conditions for a high productivity of the acid treatment process and conditions for the subsequent filtration. At a pH value less than 2.3, the amount of red mud introduced into the process and treated is small. At a pH value greater than 3.8, the subsequent filtration is difficult, primarily because of the presence of highly dispersed amorphous silica, with substantially no filtering, and the start of the separation of highly dispersed aluminum hydroxide.

(6) The method for the acid treatment of red mud was performed as follows.

(7) The original red mud contained, %: SiO.sub.2 9.3; Al.sub.2O.sub.312.4; Fe.sub.2O.sub.3 44.3; TiO.sub.2 4.4; P.sub.2O.sub.5 0.75; CaO 13.6; MgO 0.93; Na.sub.2O 2.9; K.sub.2O<0.15; V.sub.2O.sub.5 0.09; Cr.sub.2O.sub.3 0.05; MnO 0.52; SO.sub.3 2.8; rare earth metals (total) 0.14; Sc 9.0.10.sup.−3.

(8) Leaching was carried out using as the leaching agent water-soluble aliphatic carboxylic acids with fewer than 3 carbon atoms in the molecule, namely, an aqueous solution of formic acid HCOOH, an aqueous solution of acetic acid, CH.sub.3COOH, and mixtures thereof.

(9) A temperature-controlled reactor having a stirring device and pH sensor was filled with a 15% solution of formic acid and/or acetic acid, the temperature was adjusted to 80° C., and then red mud was added in small portions with continuous pH monitoring. The procedure was terminated when a predetermined suspension acidity was reached (within the pH range=1.6-4.0), but stirring was continued for another hour after the last portion of the mud was added. Next stirring was stopped and the suspension was kept at the same temperature for another hour. The solid precipitate was then separated from the liquid by filtration, after which the solid and liquid phases were analyzed to determine the extent of recovery of the most valuable components in the solution.

(10) The table below provides the recovery rates achieved by the above method for aluminum, scandium, and the rare earth metals, depending on the pH of the slurry after completion of the leaching process. The results obtained for both acids individually and for their equal-volume mixture differ insignificantly. With a shift to the alkaline side (increase in pH), a slight decrease in the recovery rate is observed, but process productivity improves at first sharply to a pH=2.3, and then more slowly to a pH=3.8. At pH=4.0 filtration becomes impossible due to the accumulation of a colloid consisting primarily of amorphous forms of silicon and aluminum compounds. As a result, it turned out that the optimal pH values at which red mud addition can be stopped are within the range of 2.3-3.8 for any combinations of acetic and formic acids.

(11) In the industrial implementation of the method, the selection of the acids is determined only by their cost and availability. Compounds of aluminum, scandium, and rare earth metals found in solution are then recovered by known methods.

(12) TABLE-US-00001 TABLE pH of Recovery in solution, % Productivity suspension after Rare earth of mud process metals acid treatment No. completion Al Sc (total) process, g/dm.sup.3 .Math. h Formic acid 1 1.6 71.5 74.4 57.2 16.7 2 1.8 71.0 73.8 56.8 102.9 3 2.3 70.3 73.1 56.2 203.7 4 2.8 69.5 72.3 55.6 235.6 5 3.3 68.8 71.6 55.0 245.7 6 3.8 67.5 70.2 54.0 248.8 7 4.0 Suspension not filtered Acetic acid 8 1.6 65.0 67.7 52.1 15.2 9 1.8 64.5 67.1 51.7 93.5 10 2.3 63.9 66.5 51.2 185.2 11 2.8 63.2 65.8 50.6 214.2 12 3.3 62.5 65.1 50.1 223.4 13 3.8 61.4 63.9 49.1 226.2 14 4.0 Suspension not filtered Mixture of formic and acetic acid in a 1:1 proportion by volume 15 1.6 67.6 70.3 54.1 15.8 16 1.8 67.0 69.8 53.7 97.2 17 2.3 66.4 69.1 53.2 192.5 18 2.8 65.7 68.4 52.6 222.6 19 3.3 65.0 67.6 52.0 232.2 20 3.8 63.8 66.4 51.1 235.1 21 4.0 Suspension not filtered