MaxR system for efficient fluosilicic acid neutralization

The treating, recycling and saving of water is becoming more and more critical in today's plants. FLSmidth's MaxR® system maximizes the settling and dewatering of slurry to free water for reuse in the process.

The treating, recycling and saving of water is becoming more and more critical in today's plants. FLSmidth's MaxR® system maximizes the settling and dewatering of slurry to free water for reuse in the process.

The treating, recycling and saving of water is becoming more and more critical in today's plants. FLSmidth's MaxR® system maximizes the settling and dewatering of slurry to free water for reuse in the process.

Water is the future's gold. Treating, recycling and saving water will be mandatory for all the plants, especially for those located in areas where water is scarce. Hydrometallurgical waste water treatment enables plant water to be saved and recycled, provided that the throughput is low in solids and polluting chemicals.

FLSmidth’s MaxR® technology, developed at the Salt Lake City technology center, can be used to treat streams in the HydroMet industry (impurities removal, acid water mine, brine clarification and heavy metals removal). Above is the typical system layout.

MaxR technology is based on mixing the suspended solids from recycled clarifier underflow slurry with base chemicals to form a coating on particles. Newly precipitated solids attach to the coating, promoting particle growth. The consequences are larger particle size distribution, more rapid solid-liquid separation, less base consumption, greater bulk density of precipitated solids and less water loss with precipitated solids.

Phosphoric acid is the key chemical in the fertilizer industry. Production from phosphate rocks leads to fluosilicic acid (FSA - H2SiF6, 10–22 wt% in water) as a by-product, which is a pollutant of primary concern that cannot be land filled without treatment.

Single-pass neutralization is an inefficient water wasting process in which base addition produces fine particles, leading to a jelly sludge where solid-liquid separation is slow. Land filling this material maximizes water loss and, as a consequence, money loss. MaxR technology means improved solid-liquid separation and maximum water recovery.

The D50, meaning 50% of the particles smaller than the particle size distribution (PSD), typically increases by 10 times. The PSD D50 increased from 3 μm to 40 µm, causing the increase in solid-liquid separation rate and minimization of water loss.

The pictures obtained via scanning electron microscope show the dramatic effect achievable when the MaxR system is used.

After an intensive laboratory and pilot scale simulation program used to identify the optimum solids recycle ratio, the first industrial unit was supplied in Saudi Arabia in 2011.

FLSmidth built the turnkey water treatment plant using MaxR technology. The plant, currently in operation, neutralizes over 100 m3/h of 18 wt% FSA and includes lime storage and milk of lime preparation, reaction tanks, a 60-meter diameter thickener, pipe racks and walkways, instruments and process control.

Suspended solids (SS) are settled efficiently to 50 wt% concentrate in the thickener, and the underflow slurry is partially recycled back to the precipitation step and partially discharged and combined with the gypsum produced in the phosphoric acid plant for disposal. The system releases 50 m3/h of neutral water, low in fluorine (< 10 ppm) and SS (< 50 ppm), which is recycled to prepare the milk of lime and the polyelectrolyte. This represents a huge savings in water cost.

A second MaxR technology plant (25 m3/h FSA at 20 wt%) is currently under construction in Jordan and is to be commissioned at the beginning of 2014.

CONTACT: Mark Mulligan