Acid pickling tanks

Treatment of Wastewater from Acid Pickling Tanks in a Galvanized Pipe... 

Acid Pickling Tanks Using Hydrochloric Acid. 1202... 

TREATMENT OF WASTEWATER FROM ACID PICKLING TANKS IN A GALVANIZED PIPE MANUFACTURING FACTORY USING SULFURIC ACID... 

MANAGEMENT AND TREATMENT OF WASTEWATER AND AIR EMISSIONS FROM ACID PICKLING TANKS USING HYDROCHLORIC ACID... 

Sulfur Mortars Hot melt-and-pour sulfur mortars are ancient, doubtless one of the oldest of all chemical resistant materials still used today. They are very resistant to non-oxidizing acids and weak alkalies below 200°F over a pH range of 0-12. Three types of sulfur mortars are typically employed (1) One containing an all-silica filler with minimum plasticizer, used to bond acid brick (2) A mortar with an all-carbon filler and minimum plasticizer, used primarily to lay carbon brick for nitric-hydrofluoric acid pickling tanks (to clean stainless steels) and the underlying floors and (3) A much more flexible all-silica filled product with double the amount of plasticizer of the other two mortars, used to join vitrified clay (terra cotta) pipe conveying waste acids and other effluent chemicals, and to assemble "pole line hardware" for the power industry. 

Typical applications include caustic storage and transportation tanks, sulfuric acid pickle tanks, chemical process and storage tanks, and miscellaneous process equipment accessories. 

After being cleaned, ware that is to be pickled is immersed successively in one or more tanks of water at 80—95°C and then transferred to the acid pickling solution. The pickling solution of 6—8% sulfuric acid is contained in a stainless steel tank or, alternatively, a lead-lined wooden tank at 60—65°C. 

Acid pickling This can be done under the following operating conditions, either with sulphuric acid (H2SO4), or hydrochloric acid (HCl). H2SO4 releases a lot of fumes and is ineffective under cold conditions. It forms iron sulphate, which forms a hard deposit at the bottom of the tank and is difficult to remove (see table on next page). 

Acid fumes, being heavy, will vaporize over the tanks. They must be vented quickly to the atmosphere through an exhaust on the pickling tank otherwise the completed phosphate surfaces may be adversely affected. Apparently, the surfaces may not show rusting immediately, but may develop it while the equipment is in operation. 

Fume scrubber water recycle. The steel finishing industry uses fume scrubbers to capture acid gases from pickling tanks. Scrubber water, which may contain a dilute caustic solution, is neutralized and recirculated continuously to adsorb the acid. Makeup water is added to replace water lost through evaporation and water that is blown down to end-of-pipe metals treatment. 

The above equation constitutes the theoretical or stoichiometric amount of liquid hydrochloric acid needed to pickle 1 ton of steel. Stoichiometric means as per chemical formula, using absolutely pure materials with no losses.16 In practice, it is not possible to use up all the acid in the pickle tank if pickling is to be complete in any acceptable time. Depending on the pickling equipment, between 70% and 80% of the free acid will be used up in dissolving the scale, and 20-30% will remain as free acid in the spent pickle liquor.16... 

When the asphalt membrane is to be used in an exposure involving acid fluorides (such as a nitric-hydrofluoric pickling solution in a pickling tank for stainless steel), the designer should specify that the polyester fabric given above be used for reinforcing rather than the above glass cloth. 

Pickle tanks can be continuous or batch processes that use sulfuric or other acids at elevated temperatures to condition and clean basic metals products. Conventionally pickle tanks are lined with two or more courses of acid-resistant brick set in a suitable acid-resistant mortar over a rubber membrane. More than one course of brickwork is usually needed to reduce the temperature to the desired level at the hot face of the membrane and to provide stability. 

The insulating power and chemical resistance of the glass block allows for a thinner lining and better membrane protection for pickle tanks where stability is not a concern. The tank is first lined with the rubber membrane, the block is bonded over that with its urethane asphalt adhesive/membrane and finally a course of acid-resistant brick laid in acid-resistant mortar is placed over the block for mechanical protection. 

Granite is used to form tank liners (bottoms, walls and covers) and skid caps and skid bars in and between tanks in continuous acid pickling lines for the descaling of steel. The acid baths are commonly 10-15% solutions of HCI or H2SO4, and FeCIs or Fe2 S04>3 at temperatures of about 200°F. The granites selected for use as skid caps and tank liners are generally quartz-rich because they are resistant to the abrasive and impact wear of the sliding steel as well as the corrosion from the acid baths. 

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