End User Focus: Liquid assets: picking the right mineral for wastewater treatment

By Siobhan Lismore-Scott
Published: Monday, 26 November 2012

Increased regulation and cost pressures mean that more than ever companies are looking to see which products better suit them. Siobhan Lismore looks at the industrial minerals used in wastewater treatment, with particular emphasis on magnesium hydroxide and lime, and speaks to key figures about how the market is progressing

There are many industrial minerals used in wastewater treatment. Some are used as filtration aids, such as perlite, bentonite, diatomite and silica sand, while others, such as lime and magnesia, are used as chemical neutralisers.

When IM last covered wastewater treatment in December 2009, a need for more products in the market was identified as industrial development was still relatively buoyant compared with today.

But the shape of many industrial minerals end markets has changed significantly in the past three years.

Construction has hit a lull as many economies have slowed down. Supply has also been interrupted in some parts of the world due to civil unrest. For example, the Arab Spring temporarily affected delivery of minerals, such as bentonite, out of Egypt.

Neutralisation

The purpose of neutralisation is to adjust the pH value to meet the requirements of the different processing units in the wastewater treatment system.

Neutralisation may be used to treat acid wastewaters containing metals. This method involves increasing the pH of the acid waste by adding an alkaline reagent to form a precipitate and then collecting the precipitate. This way, the incoming solution is pH adjusted to the optimum range for precipitating metals as hydroxides.

This process is conducted before the main step of wastewater treatment, that is clarification (or, decantation), to fulfil the overall wastewater treatment objectives.

The largest uptake on wastewater neutralising products is from the chemical and manufacturing industries. In these sectors, demand for products is still strong, Gwyn Watkins, Lhoist UK Ltd sales and logistics director, told IM.

Lhoist’s key wastewater product is the Neutralac SLS45 (see p69). This is a liquid-lime treatment for acidic effluents of all types.

“Some sectors of the market are in a deep recession, construction and steel specifically,” he said. “I think the feeling is that we are going forward to a pretty flat five years. People will need to be creative in order to expand. Business will have to be sharper.”

For now, however, demand for Lhoist’s neutralising product is still firm.

“Demand is growing. We are selling - our sales have increased by 1,000 fold since 2009. In our product, we have seen substantial growth in this year. We expect 30% more sales this year, and last year was up 80% on the previous year,” he said.

Demand is also high at US-based Martin Marietta Magnesia Specialties, which produces a neutralising agent made from magnesium hydroxide.

“We continue to see increasing demand for most of our product lines, including magnesium hydroxide,” Douglas Bopst, vice president of sales, told IM.

 
Martin Marietta Magnesia Specialties’ Manistee,
Image: Michigan manufacturing facility
Looking forward, the company agreed that “economic growth or contraction will influence demand for magnesium hydroxide”.

End markets

Most companies contacted by IM did not specifically outline which was the largest end market for its wastewater products, although it was agreed that the chemical industry formed a large part of the sector.

“It’s very difficult to say what the largest segment is,” Watkins told IM.

“It’s very diverse. We are used in a large part in the chemical industry, in water, food manufacturing and in metal treatment,” he added.

There is a split in the industry between those who believe that magnesium hydroxide is the better solution for neutralising wastewater and those that believe lime with sodium hydroxide (caustic soda) is the more suitable combination.

The arguments centre around cost, safety and supply security, and are summarised below.

Why magnesia?

US-based Premier Magnesia LLC said that while caustic soda and lime are more commonly used in the neutralisation process because they are “usually the most practical choice”, magnesium hydroxide could be the safer choice.

“Technical grade magnesium hydroxide suspensions are akin to pharmaceutical grade ‘Milk of Magnesia’ used to neutralise excess stomach acid,” Dr Mark Shand, Premier Magnesia director of technical services, said in an article, Magnesium Hydroxide - A Safer Alternative to Caustic Soda (Sodium Hydroxide), on the company website.

“They are therefore safe and non-hazardous and will not cause chemical burns. Magnesium hydroxide has found great use in treating industrial metal-laden acidic wastewater, where, compared with caustic soda or lime, will produce less sludge volume, and a filtercake that de-waters more readily,” he said.

Martin Marietta Magnesia Specialties’ Bopst agreed that there were benefits to using magnesium hydroxide.

The company produces a product called FloMag, which it describes as a safe and cost-effective method for alkalinity addition and pH adjustment of acidic waste streams.

In a white paper produced for the company titled The use of magnesium hydroxide slurry for biological treatment of municipal and industrial wastewater, Aileen Gibson and Michael Maniocha argue that magnesium hydroxide slurry “is much safer to handle than caustic soda, and does not scale equipment like hydrated lime”.

“These benefits combined make magnesium hydroxide slurry superior to caustic soda and hydrated lime when selling into the wastewater treatment industry,” the report said.

 

“Municipal wastewater treatment plants that are currently using caustic soda and hydrated lime to provide alkalinity during nitrification would be good candidates for conversion to magnesium hydroxide,” the report concluded.


Why lime?

Unsurprisingly, Lhoist Group believes its product is superior to a magnesium hydroxide neutraliser.

“The problem is that when you make slurry it doesn’t dissolve it, like with calcium hydroxide,” Watkins said.

“You have to keep it stirring otherwise it will separate out. What we have done, by changing the shape of the calcium hydroxide particle, is ensure it will stay the same, which means we can put more material in this way. Our material stays in suspension, you can put more in there and keep it in suspension,” he added.

Shand, in a second article on Premier Magnesia’s website, Storage and Handling of Magnesium Hydroxide Slurries, outlined the specifications of handling slurry.

“Some agitation is needed to keep solids in suspension while the slurry is in storage,” he said. “This can be done by a top-entering, pitch-blade turbine or rake-type agitator. Agitator shaft speed will vary depending on the impeller size and length of shaft.”

Lhoist has refined its product since 2009, Watkins added.

“The milling process has changed. [...] We have improved the processing of the lime hydrate to give it greater stability,” he said.

Demand for its products is growing, the company said, which suggests that end users are also switching to its products. This is because a lime-based solution does not require as much intervention once the solution is in place.

“A lot of companies have switched, and they found they can cut back on stirring and the amount of effort that entails,” Watkins said.

The lime used to make the product is sourced in Buxton, UK, where the company is based. It is of such high purity that it is exported to other parts of Europe and to Asia.

Regulation

A European directive was set out in 1991, which specifically dealt with wastewater treatment.

The Urban Waste Water Treatment Directive of 1991 concerned the collection, treatment and discharge of urban wastewater, and the treatment and discharge of wastewater from certain industrial sectors throughout Europe.

It set dates for end users to put in place a way to treat water discharge. These varied depending on the population exposed.

The European Commission published three report in 2004 on the implementation of the directive. The reports noted that the wastewater treatment situation in Europe was still very unsatisfactory and that none of the deadlines had been met by all member countries.

The reports also revealed that pollution parameters, such as nitrogen levels, remained high. This was down to insufficient nutrient removal by wastewater treatment plants, the reports said.

The directive represents the most cost-intensive European legislation in the environmental sector, according to the European Commission. The EU estimates that the equivalent of €152bn ($195bn) was invested in wastewater treatment from 1990 to 2010.

EU Reach (Registration, evaluation and authorisation of chemicals) regulations set out further rules on how to deal with wastewater.

Companies affected were all those which import, manufacture, repackage, formulate, supply and use water-treatment chemicals. It affects all water-treatment areas, including industrial and municipal wastewater treatment; industrial, commercial and consumer water supply treatment; and water treatment at the point of use.

CLP, or CLP Regulation, is the new European Regulation on classification, labelling and packaging of chemical substances and mixtures.

CLP is mostly concerned with the hazards of chemical substances and mixtures, and how to inform others about them. There will be an obligation to apply CLP to mixtures by 2015.

“Reach was more a health and safety issue,” Watkins said. “There’s an understanding of the material, which is more in depth. So, there’s a lot of information that has to be given.”

Reach meant that magnesium hydrate and sulphate have to be registered by 31 May 2013.

Lime substances also have to be registered. These incorporate calcium oxide, dihydroxide, calcined dolomite, calcium magnesium, and lime (chemical) hydraulic, according to the Industrial Minerals Association, which has worked with the industry in preparation for the various deadlines set out by Reach.

As well as REACH, Europe-based wastewater treatment manufacturers faced more regulation when the Industrial Emissions Directive came into force on 6 January 2011.

This directive not only affects companies such as Lhoist, which calcine lime on site and therefore use a lot of gas in order to do so, it also affects companies which have any wastewater to treat.

“When wastewaters from the cleaning of waste gases are treated outside the waste incineration plant or waste co-incineration plant at a treatment plant intended only for the treatment of this sort of wastewater, the emission limit values set out in Part 5 of Annex VI shall be applied at the point where the wastewaters leave the treatment plant,” the directive states.

“Where the wastewater from the cleaning of waste gases is treated collectively with other sources of wastewater, either on site or off site, the operator shall make the appropriate mass balance calculations, using the results of the measurements set out in point 2 of Part 6 of Annex VI in order to determine the emission levels in the final wastewater discharge that can be attributed to the wastewater arising from the cleaning of waste gases,” it continued.

“The industrial emissions directive [...] will affect us,” Watkins said. “But that is more in gasses than liquid effluent.”

While there has been a big push in regulation, there has also been an increase in information available, as well as a pressure from shareholders to be seen to be complying with environmental standards, Watkins said.

“It’s not like there’s been a big-step change, but there’s no doubt that other companies are finding more pressures. There’s a pressure from environmental regulation and water. There’s a pressure to reduce costs [É], people are aware that regulations are being applied more tightly,” he added.

Martin Marietta in the US is also subject to to tighter regulations, Bopst told IM.

“Regulatory requirements on wastewater treatment in the US continue to tighten, and will continue to have the objective of improving the cleanliness of wastewater prior to discharge,” he said.

Cost

Both Lhoist and Martin Marietta agreed there are cost pressures from their respective customer bases.

“There are always cost pressures in every facet of manufacture, including the treatment of wastewater,” Bopst said.

“Industrial companies look for ways to use less water in their process, and better recycle the wastewater they do generate,” he added.

Meanwhile, an increase in energy prices has affected costs at Lhoist, the company said.

“Energy is the biggest impact we have in manufacturing lime non-stop [...]. We have managed our gas usage as well as we can, by using recirculation shaft kilns, which make the best use of energy, for example,” it said.

The company has to use gas to power its process as it is the “cleanest” fuel. This means that the company is more also exposed to the carbon emissions trading scheme, which will be a further cost.

“One of the benefits of our magnesium hydroxide slurry products is that both economic and technical improvements are available in certain processes to help reduce effluent treatment costs,” Bopst said.

“Also, magnesium hydroxide has cost stability relative to competitive products such as sodium hydroxide,” he added.

Making the switch to magnesium hydroxide

Switching to magnesium hydroxide saw an annual saving of more than $100,000 in chemical costs at a municipal wastewater treatment plant in Kentucky, US, according to WaterWorld magazine.

The municipality used soda ash for nearly 15 years to supplement alkalinity in the biological treatment of wastewater.

The plant was attracted to magnesium hydroxide because of its improved alkalinity and because the pH levels could be controlled. This is important in the state of Kentucky where an upper discharge limit of pH 9.0 cannot be exceeded.

There was also a concern about the long-term availability of soda ash as well as the cost of water spray to mitigate the toxic zone foam caused by soda ash. The switch was made in 2007.

After initial tests, the facility then switched to lime slurry in 2009, after a water treatment consultant said it could save even more money (quoting a figure of $370,000). But “the city came to realise that the costs associated with lime’s operational issues outweighed the chemical cost savings”, WaterWorld reported.

The city’s treatment plant experienced excessive scaling, which led to flow interruptions, plugging of lines and pipe fittings, and equipment failures. The plant also experienced a large increase in solids at the belt filter presses, which required increased landfill disposal.

The plant reconverted to magnesium hydroxide in 2010.

Heavy metal and fluoride removal from wastewater in the metal plating industry

A leading global automotive supplier in France uses the Henkel process to give the different components in its heating, ventilation and air-conditioning systems anticorrosion and hydrophobic properties.

The wastewater generated by this operation contains heavy metals and fluoride. The plant used a combination of NaOH for the neutralisation and CaCl2 for the precipitation of fluoride and heavy metals to treat the effluents before discharging them into a river.

The resulting CaF2 and metal hydroxides were then removed by flocculation and filtration.

However, this did not always prove effective in meeting the maximum fluoride concentration (15 mg/l) imposed by the local authorities.

Lhoist offered a new method for treating the wastewater:

- Getting the pH at the entry of the process to a value of 6.5 and maintaining it at that level instead of having the former fluctuations which ranged between 5 and 12;

- Increasing the pH during the treatment phase from 8 to 9.5 for a better precipitation of the fluoride; and

- Simplifying the process by using a single reagent instead of a combination of NaOH and CaCl2.

Costs in other minerals used in wastewater treatment

In other minerals used in wastewater treatment, the costs are well documented.

Imerys, the world leader in filtration minerals such as perlite and diatomite, said in November that it will be increasing European and US prices for perlite and diatomite products by between 4% and 8%, effective 1 January 2013.

“Price increases are necessary to achieve a sustainable product platform and meet customer demand,” the company said.

Perlite is used in wastewater treatment in its expanded milled form. Expanded perlite has rough edges and curved surfaces, which interlock to form an effective filter bed that does not compact.

Diatomite, meanwhile, is mainly used in beverage and food production, but it is also used in water filter applications. Diatomite has a large pore and void

volume and, therefore, a high degree of permeability. It is chemically inert, lightweight and can retain up to 90% of its void space during compression.

The last Imerys price rise in perlite and diatomite took place in January 2012. At that time, the French company raised prices by between 3% and 5% for European customers.

The company’s Celite plant in Murat, France, meanwhile, applied an energy surcharge on all its goods, charging €25.50/tonne for November 2012. Celite is a brand of diatomaceous earth.

The charge was last applied in August 2012 at a rate of €25.50/tonne ($31.29/tonne), which was a drop of €10.20/tonne from surcharges applied in May 2012.

Rising fuel and gas costs are the main causes of the rising energy costs, Imerys said, and left the company with “no alternative but to implement [the energy surcharge]”.

Freight, packaging and raw materials have also impacted Imerys’ business dramatically, the company added.

Freight is often what the bentonite market points to as being an added cost pressure.

Bentonite is used as a flocculent in the purification of wastewater, isolating and removing oils, heavy metals and suspended solids. This is by no means the largest market segment for bentonite (see p40), but it is a growing sector for the mineral.

AMCOL International Corp., one of the world’s largest producers of bentonite, has surface modified bentonite clay to produce a filtration media that removed mercury from water, rendering it soluble and non-toxic.

New markets?

Lhoist is always seeking new areas to expand into, it said. As well as being used in wastewater treatment, its Neutralac SLS45 product has been sprayed on asphalt to avoid cracking and also used as a foot bath for cattle, Watkins said.