Complimentary calcium fractionation techniques to increase coproduct solids value and utilization

Abstract Text:

Soluble and precipitated calcium can be fractionated from other solids by utilizing complimentary techniques. Our research is focused on combinations of cross flow filtration together with mechanical separation via a sanitary hydrocyclone. We hypothesize that larger CaP particles are more abrasive for dairy equipment than the smaller particles. Hydrocyclones can remove large (>50 micron) particles of CaP precipitate, before utilizing high temperature compatible, large MWCO ultrafiltration and microfiltration elements to purify and concentrate the smaller sized CaP precipitate from acid whey coproducts. Deproteinized acid whey (UF permeate) was subjected to nanofiltration (NF) to reduce the volume and impurities (lactic acid, simple sugars & monovalent ions), which increased the calcium and phosphate concentrations. Optimal conditions for the precipitation of calcium phosphate by a combined heating/neutralization step were established as temperature 60-70°C and pH 7.0. CaP precipitates were fractionated on the basis of particle size using a sanitary hydrocyclone. We studied the impact of hydrodynamic conditions (vessel shape, agitation) on CaP precipitate size range and separation efficiency of hydrocyclone. It was observed that when neutralization/heating was done in vessels with less turbulence the CaP particle size was bigger, which increased the hydrocyclone separation efficiency. Another significant finding was that hydrocyclone overflows from both low turbulence and high turbulence tanks have very similar particle size profiles. Apex nozzle size of the hydrocyclone did not impact the separation efficiency. The small CaP particles classified into the hydrocyclone overflow, were purified and concentrated using various wide pore membrane sizes of high-temperature-compatible UF and MF elements (Microdyn DS-UV200-3838(200kDa), DS-MP005-3838(0.050μm) & DSMP020-3838(0.20μm)) membranes. It was found that the separation efficiency of CaP by either UF, or MF, was much better than centrifugation, as the total Ca contents in the centrifugal supernatant and MF permeate were 47.9 and 16.7 mg/100g, respectively. Milk mineral concentrate with small, and relatively narrow, particle size range, and high CaP purity was obtained using this process (composition: 76.7% ash, 30.2% calcium and 16.1% phosphorus (solids basis)). Study of the abrasiveness of CaP precipitate in relation to its particle size is currently in progress.

Keywords: Coproducts, hydrocyclone, milk minerals, acid whey