A Mexico salt mine improves production with custom equipment

Waves of deep pink waters greet visitors as they arrive at Las Coloradas, located on the northern edge of the Yucatán Peninsula, Mexico. For visitors from Cancun the trip has been about three hours to see the brightly colored salinity concentration ponds and associated solar salt production that is a growing Las Coloradas tourist destination.

The salinity concentration ponds and surrounding land belong to Industria Salinera de Yucatán S.A. de C.V. (ISYSA), a solar salt extraction mining operation that harvests up to 840,000 tons of salt a year at this site. That’s about one-third of Mexico’s annual salt consumption. The company packages and sells its salt in about 50 different products, primarily in Mexico, with some going to other Central American countries.

The solar salt extraction operation is located in an ecological preserve, Parque Natural Ría Lagartos. This means the company can’t expand or create new salt concentration ponds for salt production. A special ISYSA department works with government and environmental organizations to monitor and preserve the coastal wetland’s flora and fauna. This includes more than 210 documented species of birds that are also a big tourist attraction, including thousands of flamingos.

The salt production is perhaps the greatest natural wonder at the site, in addition to the striking color of the water. The 5,691-acre operation is a marvel of natural processes, working in harmony with the environment and limited mechanical assistance. The founder realized the potential of the location in 1946 after noticing salt crystals forming naturally. Aside from the natural salt formations, the founder also chose the location for its perfect blend of elements: minimal rain, high sun exposure and ample wind.

“When it comes to a good harvest, sun and wind are our best friends,” said Felipe Pérez Peralta, ISYSA Sub-gerente de Campo. “We don’t get a lot of rain, but when we do, it can set harvest back a year and cost as much as US$6 to US$8 million in lost production.”

The salt harvesting process begins with water flowing from the Ría Lagartos estuary into a 12.4-mile chain of ponds connected by pumps and canals. The first stop is a string of 26 evaporation ponds where the water is held until evaporation begins, thus increasing its salinity. As the water reaches optimal temperature and salinity, ISYSA uses a series of pumps to move the water to 15 crystallizer ponds.

The crystallizer ponds are famous because of their pink color. The vividness is due to pigmented protein from a microbe known as Halobacterium, a single-celled organism that thrives where nothing else can survive in high salinity water levels (4m NaCl or higher).

In the crystallizer ponds, the water continues to get saltier and as a result of the higher concentration of brine, hotter. As the water reaches temperatures approaching 104 F a combination of the high salt levels and temperature allows salt crystals to form at the bottom of the ponds. When conditions are right and there is no rain, salt crystals can form at rates of 1.5 inches a month. ISYSA lets salt crystallization continue until the layer of salt reaches 3 to 4 inches thick and then drains a pond. What’s left behind is a field of white salt which at first glance could easily be mistaken for snow.

Harvesting fields of salt
The salt harvesting operation kicks into high gear as soon as the salt crystals are exposed. ISYSA harvests salt twice a year with the first and largest harvest beginning around March or April and the second around September or October.

Once kicked off, the salt harvesting operation runs 24/7. The harvesting is completed as quickly as possible to avoid rainfall. Rain, or even worse, a hurricane, can significantly set harvest back by dissolving salt crystals and adding fresh water to the ponds.

In the harvesting phase, the operation begins by using a motor grader to push salt into 10- to 14-inch-high windrows. The grader operator leaves about 1 inch of salt on the bottom of the pond to avoid mixing dirt from the pond bed with the harvested salt. A heavy-duty conventional farm tractor follows, pulling a special salt harvester capable of picking up the salt windrows and conveying the salt into a hauler, harvesting 330 tons of salt an hour. The unit works by scooping salt from the salt windrows onto a conveyor which transfers the material into a bottom dump trailer pulled by a conventional off-highway truck/tractor. Three custom-engineered tractor trailers constantly rotate between the salt harvester and the raw salt processing plant, ensuring continuous salt harvesting and as little harvesting downtime as possible. When a trailer is filled to about 66 to 80 tons the harvester briefly stops, the loaded trailer pulls away and the next trailer is pulled into position before the salt harvester resumes operation.

The bottom dump trailers dump the salt into a hopper connected to a salt washing and processing plant. The processing plant rinses the salt using saturated salt brine to prevent any harvested salt from dissolving. Connected conveyors then dump the salt into massive piles that rise up to 45 feet above the landscape.

This harvesting process has improved considerably over the years. Until 2013 ISYSA used five on-highway bottom dump trailer trucks with capacities of 14.5 tons or 28.5 tons. The trucks’ low capacity slowed salt harvesting production. Using the five trucks, just 4,500 tons of salt could be harvested on a really good day, with the first harvest of the year taking about five months to complete. Salt harvester idle time was high as the trucks filled up quickly and the salt harvester was constantly stopping and starting.

Because much of the harvested salt is meant for human consumption, it is also very important that there are no harvesting equipment fluid leaks or equipment contaminants lost in ISYSA’s salt harvesting process. Thus, the first shift every day carefully cleans and inspects harvesting equipment for any issues.

With the exposure to the extremely corrosive salt environment, the previous on-highway bottom dump trailer trucks required regular repairs, particularly involving the pneumatic door cylinders. The previous trucks were down for maintenance up to 30% of the time.

ISYSA management realized that adding new efficiencies to the process was important for the future of their operation. They also wanted to limit the environmental impact by reducing needless idle time while using tractors that are more efficient and decrease emissions.

Finding a new bottom dump trailer
ISYSA management knew that the long-term success of the salt mine relied on finding a more efficient trucking solution. That solution required higher capacity bottom dump tractor trailers that could handle the desired salt production. Management sought out Philippi-Hagenbuch, Inc in 2012 and requested a solution to double their salt production and minimize maintenance issues. The Peoria, Illinois-based manufacturer designs and builds such custom equipment for off-highway haul trucks.

The two companies worked together to assess ISYSA’s needs and design a suitable bottom dump trailer. The trailer needed an 80 ton load capacity. Trailer components would also have to be able to withstand the corrosive salt environment and require only minimal maintenance. Additionally, the tractor trailer needed to be fairly narrow and have a lower load height than a typical 80-ton-capacity bottom dump trailer to accommodate ISYSA’s existing salt harvester. Following initial design discussions, PHIL representatives visited Las Coloradas to see ISYSA’s salt harvesting and processing plant firsthand and to determine the full design-scope and engineering requirements for the fully customized project to become a reality.

In 2013, PHIL delivered three custom engineered bottom dump tractor trailer trucks to ISYSA. To fit ISYSA requirements and to match with the existing salt harvester, the 80-ton-capacity trailers were 42 feet long, 14 feet wide, 11 feet high, included a struck volume of 61 cubic yards and a 2:1 heaped volume of 75 cubic yards. The trailers also initially featured long goosenecks designed for proper weight distribution with the three tractors ISYSA ordered to pull them.

To minimize the effects from the corrosive salt hauling environment and to protect the salt hauling areas of the bottom dump trailers, PHIL used a unique Duracorr stainless steel plate.

Additionally, SSAB’s Hardox® 450 high-strength steel was used for the overall trailer structure, consequently minimizing overall bottom dump trailer weight. Lowering trailer weight and associated ground pressures in the drained salt ponds was yet another important ISYSA concern to prevent risks of the equipment getting stuck in the soft pond beds.

In order to achieve an 80-ton capacity and a low load height, PHIL designed the trailers with vertical side walls instead of common inward sloping side walls. A teepee-shaped structure lengthwise in the center of the trailer accommodated full-trailer-width clamshell doors, which facilitate even and quick “full” trailer-width material dumping.

A single hydraulic cylinder controls the trailer’s clamshell doors as opposed to the typical two pneumatic cylinders featured on ISYSA’s old trucks. The single cylinder opens both doors in unison, minimizing trailer rocking that can happen as a result of opening only one door at a time. The doors also feature an over-center door locking system which minimizes forces on the door’s hydraulic control cylinder when the trailer is loaded.

It wasn’t long before ISYSA noticed big improvements resulting from the new bottom dump trailers. Daily production doubled to a steady 9,000 tons per day with the three new trailers. In addition, the first harvest of the year now takes only about three months as opposed to five months with previous equipment.

“Philippi Hagenbuch has always been a custom solution provider,” said LeRoy Hagenbuch, Philippi-Hagenbuch co-founder and chief engineer. “These trailers are a great example of our custom engineered approach. ISYSA had a need they wanted to solve. They looked at other manufacturers, but no one was willing or able to develop a solution. We understood their problem and worked closely with them until we could deliver exactly what they were looking for.”

The mine’s maintenance department also took a liking to the new equipment. PHIL built the trailer with all vulnerable parts sealed from the corrosive environment. The single door cylinder and hoses are protected and require no greasing or maintenance. The trailers use rugged 3-inch pins surrounded by half-inch wall bearings for all door pivots. In addition, the trailers have sealed, oil-cooled disc brakes and an oil brake control line, both of which minimize the risk of leaks.

“Maintenance is minor on the PHIL trailers, especially compared to the pneumatic cylinders on the old equipment. Those previous trucks had a number of mechanisms that often broke down,” said Mario Guzman, Jefe de Transporte. “We went from the equipment being broken for 30% of the time to excellent up-time with the new bottom dump trailers.”

Though happy with the new bottom dump trailers, ISYSA did have problems with the used trailer tractors they had originally chosen for this project. The used tractors required a lot of maintenance and were not the ideal choice for the environment. When management looked into purchasing new Caterpillar tractors, they again reached out to PHIL for help customizing the new tractors to work with their PHIL Bottom Dump Trailers. PHIL agreed, developing and sending the Las Coloradas operation kits to install fifth wheel hitch arrangements on their new Caterpillar tractors’ chassis. The kits PHIL supplied also included components to modify the length of the bottom dump trailer tongues to optimize weight distribution on the updated truck-trailer-chassis combination.

Hauling with success
ISYSA management said the improved production speed and reduced maintenance from the new tractor trailers have helped ensure a fast return on their equipment investment. Instead of having to scramble to keep up with the salt harvest and stay ahead of weather issues, crews now periodically finish harvesting salt ponds faster than others can be drained. This has led plant management to look for further ways to increase salt production.