Patent GB-824081-A (GB)
Title: Improvements relating to treatment of liquid such as the effluent from a plating plant
Inventor: AINSWORTH FRANK GLAVE
IPC: G05D21/02
Filed: 1956-04-24
Abstract: 824,081. Electric tests. BRITISH THOMSON-HOUSTON CO. Ltd. April 24, 1957 [April 24, 1956], No. 12529/56. Class 37. In an apparatus for controlling the introduction into a liquid flow of a chemical treating a solute in the flow, a sample of the flow in an electro - chemical cell is titrated until the voltage output from the cell is a predetermined value, while the solute treating chemical is added to the flow of a rate determined by the amount of titrating solution added and the rate of flow. The invention is described with reference to neutralizing cyanide in the output from a plating bath. A sample is taken from the effluent and quantities of lead acetate and caustic soda are added to precipitate halides and metals. Silver nitrate is then added in measured quantities, each addition adjusting a valve controlling the addition of permanganate or other oxidizing agent to the effluent. The amount of permanganate is also controlled in accordance with the rate of flow of the effluent. When the E.M.F. of a test cell immersed in the test solution is zero the supply of permanganate ceases. Detailed operation (Fig. 1).--At the start of a cycle cam-shaft 2 tilts beaker 4 which is flushed out and restored and one of cam-operated switches 7 causes pump 6 to introduce a measured quantity to the beaker. The contents of the beaker are agitated by compressed-air and cam-shaft 1 operates pumps 21, 22 to introduce lead acetate and caustic soda to precipitate halides and the metals and ensure that the solution is alkaline. Shaft 1 stops and test shaft 23 rotates and at each revolution cam 25 operates pump 24 to add a quantity of 0.01% silver nitrate solution to the beaker and the cam 27 steps a double ratchet mechanism to open valve 26 controlling the supply of permanganate to the effluent. At the same time the valve is opened by a flow meter of the type described in Specification 824,082, [Group XL (b)], which produces a number of pulses proportional to the rate of flow to operate a solenoid sl and step on a further ratchet arrangement. The valve is of a type which combines these two movements. Cam-shaft 23 continues rotating and adding further silver nitrate and adjusting valve 26 until the output of the cell in the beaker is zero when it stops. If, after a predetermined number of tests, the output of the cell is not zero, engagement of a thread 38 on the shaft with a ratchet 37 will have moved cam-shaft 23 axially sufficiently for a cam 35 to introduce a stronger solution of silver nitrate while cam 25 is out of action. At the same time cam 36 will step the ratchet controlling valve 26 a correspondingly greater distance. The mechanism moving the shaft axially may be as described in Specification 824,083, [Group XXIV]. When the E.M.F. output of the cell is zero the main shaft is restarted to operate pawl 40 so that member 42 may drop to the new position of member 41 if the amount of silver nitrate introduced has decreased from the previous test. Solenoid s4 is operated to allow shaft 23 to reset axially while solenoids s2 and s3 allow first the member 45 to drop to member 44 and member 44 to restore to its original position. Tests may be made on the effluent after treatment by means of changeover valve 11. The test cell, Fig. 2.-Beaker 4 contains a silver electrode 14 immersed in the effluent 13 and the lower end of a tube 15 closed by a porous plug 16 containing a further silver electrode 17 and a saturated solution of silver chloride in saturated potassium chloride solution. This latter solution is kept saturated by potassium chloride crystals 18. This arrangement constitutes effectively two half cells, one a silver-effluent system and the other a silver chloride-silver system. When the concentration of positive silver ions in the effluents being titrated becomes equal to that for the silver chloride solution the total output of the cell is zero.