Calcium filtration process equipment

Lime-Sulfuric. Recovery of citric acid by calcium salt precipitation is shown in Figure 3. Although the chemistry is straightforward, the engineering principles, separation techniques, and unit operations employed result in a complex commercial process. The fermentation broth, which has been separated from the insoluble biomass, is treated with a calcium hydroxide (lime) slurry to precipitate calcium citrate. After sufficient reaction time, the calcium citrate slurry is filtered and the filter cake washed free of soluble impurities. The clean calcium citrate cake is reslurried and acidified with sulfuric acid, converting the calcium citrate to soluble citric acid and insoluble calcium sulfate. Both the calcium citrate and calcium sulfate reactions are generally performed in agitated reaction vessels made of 316 stainless steel and filtered on commercially available filtration equipment. 

The calcium cyanamide feed is weU mixed with the recycled slurry and filtrate ia a feed vessel. The calcium cyanamide is added at a rate to maintain a pH of 6.0—6.5 ia the cooling tank. The carbonation step can be conducted ia a turbiae absorber with a residence time of 1—2 min. After the carbonation step, the slurry is held at 30—40°C to complete the formation of calcium carbonate, after which the slurry is cooled and filtered. AH equipment for the process is preferably of stainless steel. The resulting solution is used directiy for conversion to dicyandiamide. 

From the final pond the concentrated brine (Table 1.3) with a density of about 1.25 g/cc was pumped nearly 4.8 km (3 mi 1.5 mi in 1967, Gadsby, 1967) to the processing plant in the town of Silver Peak. The plant had been converted from a silver ore cyanide-leach plant that had operated there from 1864-1961. In the conversion all of the tanks and settlers were rubber lined to reduce iron contamination in the product, and considerable new equipment was added. The solar pond brine was first reacted with lime to remove most of the residual magnesium and some of the sulfate and borate ions, and then a small amount of soda ash was added to precipitate most of the calcium from the lime reactions. The slurry from these operations was settled and filtered, and the overflow solution sent to storage tanks. From there the brine was pumped through filter presses to be totally clarified, and then heated to 93°C (200°F lithium carbonate has an inverse solubility) and reacted with dry soda ash and hot wash and make-up waters to precipitate the lithium carbonate product. Extra water was added to prevent salt from crystallizing, since the pond brine was samrated with salt. The lithium carbonate slurry was thickened in a bank of cyclones, and the underflow fed to a vacuum belt filter where it was washed and dewatered. The cyclone overflow and filtrate were... 

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