Process and an apparatus for recovering arsenic trioxide from gases

Claim 2

IN A PROCESS FOR RECOVERING ARSENIC TRIOXIDE FROM A GAS WASHING OUT SAID OXIDE FROM THE GAS WITH A LIQUID HAVING THE ABILITY OF DISSOLVING ARSENIC TRIOXIDE, SAID OXIDE BEING RECOVERED FROM THE OBTAINED SOLUTION THEREOF BY CRYSTALLIZATION FROM A SATURATED SOLUTION, THE IMPROVEMENT WHICH COMPRISES REMOVING NON-DESIRABLE DEPOSITS IN THE APPARATUS FORMED IN CONNECTION WITH THE SATURATED SOLUTION BY DISSOLUTION WITH AN UNSATURATED SOLUTION, THE IMPROVEMENT WHICH COMPRISES REUNDER A CONTINUOUS SUPPLY OF GAS.

Claim 3

The process according to claim 1 further comprising operating in one and the same recovery system with alternatingly saturated and unsaturated solutions of arsenic trioxide.

Claim 4

The process according to claim 1 wherein the washing out and crystallization are carried out in at least two systems operated in parallel, one system being operated under saturation with regard to arsenic trioxide, and the other system being operated under an unsaturated condition, the operational conditions of the system being shifted from time to time so as to prevent excessive build-up of deposits of arsenic trioxide.

Claim 5

The process according to claim 3 further comprising washing the gas continuously in a first system with an essentially saturated solution of arsenic trioxide, partially evaporating in the first system the essentially saturated solution to obtain precipitation of arsenic trioxide, removing the precipitated arsenic trioxide from the system, continously washing the gas in a second system with an unsaturated solution of arsenic trioxide, adding to the second system, liquid in an amount to maintain unsaturation in the solution, transferring unsaturated solution from the second system to the first system, and, when arsenic trioxide has formed a non-desired deposit in the first system, operating said system with the unsaturated solution to dissolve the deposit and operating the second system with an essentially saturated solution.

Claim 6

The process according to claim 3 wherein the dissolution of the non-desired deposits is carried out only for a time period sufficient to leave a corrosion-protecting layer.

Claim 7

In an apparatus for recovering arsenic trioxide from a gas containing the same, said oxide being obtained by crystallization from a saturated solution used to scrub the gas, and being of the type composed of at least two scrubbers (1A; 1B) coupled in parallel, and associated crystallizers (6A; 6B) and gas coolers (2A; 2B) and conduit means for maintaining a circulation system of wash liquiD for each scrubber, a common pump receiver (3) divided into sections (3A; 3B), and one section for each circulation system, the improvement which comprises conduit means (8) and switching means (10A; 10B) for passing liquid condensed in the gas coolers (2A; 2B) to the section (3A) containing unsaturated solution, and means (12) for transferring solution from section (3A) to section (3B) containing a saturated solution.

Claim 8

In an apparatus for recovering arsenic trioxide from a gas containing the same, said oxide being obtained by crystallization from a saturated solution used to scrub the gas, and being of the type composed of at least two scrubbers (1A; 1B) coupled in parallel, and associated crystallizers (6A; 6B) and gas coolers (2A; 2B) and conduit means for maintaining a circulation system of wash liquiD for each scrubber, a common pump receiver (3) divided into sections (3A; 3B), and one section for each circulation system, the improvement which comprises conduit means (8) and switching means (10A; 10B) for passing liquid condensed in the gas coolers (2A; 2B) to the section (3A) containing unsaturated solution, and means (12) for transferring solution from section (3A) to section (3B) containing a saturated solution.

Claim 9

Apparatus according to claim 6, characterized in that said transfer means consist of partition walls (12) arranged between the sections (3A; 3B) which in both directions act as over-flows.

Claim 10

An apparatus according to claim 6, characterized in that said switching means consists of openable and closable valves (10A; 10B), respectively, whereby liquid condensed in the gas coolers (2A; 2B) can be passed to the section(s) (3A), containing unsaturated solution.