Non-polluting system for metal surface treatments

A cyclic mechanical impact plating process for plating consecutive batches of base metal articles without liquid discharge of econologically objectionable liquid effluent from the process and with reclaiming of substantially all treating water withdrawn from various stages of the process wherein

• A. each process cycle comprises the steps of
• a. loading a batch of base metal articles having a known total surface area into a tumbling zone;
• b. loading a mass of impacting media and an aqueous inorganic cleaning acid solution into said tumbling zone and agitating the resulting mixture in said tumbling zone until the articles are cleaned;
• c. draining the spent acid solution from the tumbling zone and passing it to a spent acid storage zone;
• d. adding an aqueous solution of a water-soluble copper salt to the cleaned articles and impacting media and agitating the resulting mixture in the tumbling zone until copper metal plates out onto the metal articles;
• e. draining the spent aqueous copper solution from the tumbling zone and passing it to a spent copper solution storage zone;
• f. adding water, promoter chemicals containing a soluble tin salt, acid and a buffer for keeping the resulting aqueous mixture in the tumbling zone at pH between about 2.5 and 4 and agitating the metal articles, media and aqueous mixture;
• g. adding a malleable metal powder selected from the group consisting of zinc, cadmium, brass, copper, aluminum, tin, lead, gold and silver to the mixture in the tumbling zone in an amount which is at least 1 to 75% in excess over the amount of metal required to deposit a predetermined thickness of said malleable metal uniformly over said metal articles and agitating the resulting mixture of solids and plating liquid in the tumbling zone for a time empirically predetermined to provide a malleable metal plating of predetermined thickness on said metal articles while the plating liquid becomes depleted;
• h. removing the depleted plating liquid including metal powder suspended therein from the tumbling zone and passing it to a plating liquid storage zone;
• i. adding rinse water to the plated metal articles and impacting media in the tumbling zone and agitating the mixture to effect rinsing of the plated metal articles;
• j. removing the used rinse water from the tumbling zone and passing it to a rinse water storage zone;
• k. removing the plated metal articles and the impacting media from the tumbling zone and separating the articles from the media;
• l. storing the separated media in a media storage zone;
• m. recovering the plated metal articles;
• and
• wherein
• B. another cycle comprising steps (a) through (m) is started upon loading a new batch of base metal articles to the tumbling zone in step (a), returning to said tumbling zone in step (a) of the last mentioned cycle the spent acid solution from the spent acid storage zone and adding a make-up amount of cleaning acid thereto to insure proper acidity for cleaning the metal articles;
• also returning to the tumbling zone in step (a) the media from the media storage zone;
• returning to said tumbling zone in step (d) the spent copper solution from the spent copper solution storage zone and adding a make-up amount of copper solution thereto;
• returning to the tumbling zone in step (f) the spent plating liquid and metal powder from the plating liquid storage zone and adding make-up amounts of promoter chemicals and malleable metal powder thereto;
• and returning to the tumbling zone in step (i) the previously used rinse water from the rinse water storage zone and adding a make-up amount of rinse water thereto;
• and wherein
• C. additional cycles comprising steps (a) through (m) are repeated a number of times until process performance drops to a predetermined minimum, at which stage the plating liquid containing suspended and dissolved metal compounds is rectified by adding alkali thereto, the resulting precipitate is mechanically separated from the rectified liquid and the rectified liquid is used in another cycle of the process after acidifying it to a pH of not more than 6.