Molybdenum pickling

The effluents mentioned are formed in the course of production of tungsten spirals used as filaments for electric bulbs, during the pickling of molybdenum foil, sheetmetal, or in other processes of molybdenum pickling. Tungsten spirals are made by coiling... 

We undertook work to design simple and economical methods for the recovery of molybdenum, copper, and manganese from industrial solid wastes and utilization of pickling effluents [1,2, 9]. 

Fig. 2. Scheme of molybdenum recovery from industrial acid pickling effluents. 

MOLYBDENUM RECOVERY FROM ACID PICKLING EFFLUENTS... 

The proposed method for the recovery of molybdenum from the effluent in question [14, 15] consists of a two-stage neutralization of the pickling mixture with ammonia water or ammonia gas (Fig. 2). The mixture is first neutralized to pH 2 (1). Precipitated molybdates are filtered (2) and the solid form (3) after purification (4) and crystallization gives the end product (5). The liquid after filtration may be neutralized to pH 7-8 (6) and may serve as a liquid fertilizer (7) or it may be concentrated (8) crystallized (9), filtered (10), and dried (11) to the solid ammonium sulfate and nitrate enriched with molybdenum (12). 

Alloys containing molybdenum can potentially experience catastrophic oxidation. The super-austenitic stainless steels such as Alloy AL-6XN, a 21Cr-25Ni-6.5Mo-N alloy (UNS N08367), are an example. A heavy molybdenum oxide scale forms, usually as a result of an improper heat treatment or a severe thermal excursion. Removal of such scales prior to service (or return to service), usually by pickling, prevents this problem. 

Table 4.89. Pickling, descaling, and etching procedures for molybdenum and its alloys ...

The chromium-nickel-molybdenum steels 1.4571 (SAE 316 Ti, X6CrNiMoTil7-12-2) and particularly 1.4435 (SAE 316 L, X2CrNiMol8-14-3) are resistant to crevice corrosion, which can occur under the operating conditions in a digester if steels with lower alloy contents are used. The importance of the correct constructive design as well as the elimination of welding tarnishes by pickling is discussed [58]. 

The body contains 8-10 mg of molybdenum. Daily intake in food is approx. 0.3 mg. It is a component of aldehyde oxidase and xanthine oxidase. The bacterial nitrate reductase involved in meat curing and pickling processes contains molybdenum. High levels of the metal are toxic, as has been shown by cattle grazing on molybdenum-enriched soil. The grass on such soil contains 20-100 pg molybdenum/g dry matter. 

Pickling bath Molybdenum disulfide with grease 94 17 7 Smooth... 

Pickling bath(a) Molybdenum disulfide with grease 70 7 1 Smooth... 

Applications. Alloy 20 is a highly alloyed iron-base nickel-chromium-molybdenum stainless steel developed primarily for use in the sulfuric acid-related processes. Other t5fpical corrosion-resistant applications for the alloy include chemical, pharmaceutical, food, plastics, synthetic fibers, pickling, and FGD systems. 

---