Sulfuric acid Sludges

The sulfuric acid sludge from sulfuric acid treatment is used frequently as a source (through thermal decomposition) to produce sulfur dioxide (SO2, which is returned to the sulfuric acid plant) and sludge acid coke. The coke, in the form of small pellets, is nsed as a snbstitute for charcoal in the manufacture of carbon disulfide. Sulfuric acid coke is different from other petrolenm coke in that it is pyrophoric in air and also reacts directly with snlfnr vapor to form carbon disulfide. 

Waste sulfuric acid sludges from petroleum refineries are disposed of by conversion to S02 for production of fresh sulfuric acid. The heavy organic components of the sludges can be decomposed thermally at 800-1300°C (Lurgi, Monsanto Enviro-Chem) or reduc-tively at 200-600°C with coal in a rotary kiln (Chemico). Thermal decomposition is accom-... 

Most methyl methacrylate (MMA) is made by the acetone cyanohydrin process. Developed in the 1930s for the production of MMA from acetone, hydrogen cyanide, sulfuric acid, and methanol, it has been improved over the years, but problems inherent in the basic process persist. For example, production of large quantities of ammonium bisulfate by-product and sulfuric acid sludge, as well as difficulty in obtaining low cost sources of... 

The cake produced by the digestion is extracted with cold water and possibly with some diluted acids from the subsequent processes. During the cake dissolution it is necessary to maintain the temperature close to 65°C, the temperature of iron sulfate maximum solubiUty. To prevent the reoxidation of the Fe " ions during processing, a small amount of Ti " is prepared in the system by the Ti reduction. The titanium extract, a solution of titanium oxo-sulfate, iron sulfate, and sulfuric acid, is filtered off. Coagulation agents are usually added to the extract to faciUtate the separation of insoluble sludge. 

Copper-plating bath compositions of various types have been used. A typical bath formulation consists of 200 g copper sulfate crystals, 30 mL cone, sulfuric acid, 2 mL phenylsulfonic acid, and 1000 mL distUled water. A pure copper anode may be used a copper anode containing a trace of phosphoms reduces sludge accumulation in the plating bath. 

Hydrofining has all the advantages of acid treating without the disadvantages. For example, acid treating does not readily remove refractory sulfur compounds such as thiophene the treated products must be rerun to remove polymers with a consequent yield loss and disposal of the acid sludges is a serious problem. 

It is useful to treat the raffinate to recover the two acids it contains. The raffinate can first be subjected to a thermal treatment which decomposes it into insoluble metallic oxides, hydrofluoric acid and sulfuric acid. In a first scrubbing, sulfuric acid is recovered, whilst in a second stage, hydrofluoric acid is absorbed. When put into operation, this process not only causes a reduction in the amount of sludges but also leads to acid production for return to the process. 

Dilute sulfuric acid Electrolytic cell slimes/sludges... 

Chlorinating the aqueous waste sludge suspension (to oxidize the chromium) at temperatures of 20 to 80°C and pH values between 4 and 13. The chlorinated sludge is then acidified with sulfuric acid to a pH of 1.0 to 3.0. The insoluble components are then separated, followed by the separation of the chromium(VI) from the solution using a fixed-bed anion exchanger (at pH values of <3). 

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