Here are two I think will recover strongly from current weakness and deliver excellent long-term returns for my portfolio.

Science in Sport

Price: 54p per share
Market cap: £77m

Broader demand for goods and services drops when times are tough for consumers. But I believe Science in Sport (LSE: SIS) might prove more resilient than many UK shares. This penny stock manufactures protein powders, energy gels, and other nutritional supplements that help keep sporty people going.

People don’t drop their sports and fitness goals when times get tough. Even if they can’t afford to go to an expensive gym they can switch to a low-cost operator. Or they can work out in other ways like road running using home fitness equipment. So I’m expecting demand for Science in Sport’s products to remain solid.

From a growth perspective, I like the firm’s strategy of developing the brand through partnerships with elite sports teams and organisations. It has teamed up with 330 such bodies, and progress with NBA basketball and NFL football teams in 2021 helped drive US revenues 50% higher last year.

Intense competition is likely to remain a threat to Science in Sport. But I’m convinced the company could still deliver terrific shareholder returns from its rapidly growing market. Grand View Research analysts think the sports nutrition sector will almost double in size between now and 2030 (to $82.3bn).

AfriTin Mining

Price: 6.8p per share
Market cap: £75.7m

Commodities producers like AfriTin Mining (LSE: ATM) aren’t usually popular shares when economic conditions worsen. The prices of the stuff they produce can fall off a cliff when fears over demand increase. AfriTin’s recent rapid price declines illustrates this point and poses a big threat to this particular mining stock.

I’m still thinking of buying AfriTin shares today though. This is because I’m focussed on the company’s long-term profits outlook and I expect sales of its tin to rocket in the years ahead. I’m tipping consumption of the soldering metal to increase as demand for consumer electronics surges.

I think this tin miner could be an especially lucrative way to exploit the coming ‘commodities supercycle’ too. For one, expansion of its flagship Uis project in Namibia should lift tin production significantly in the years ahead. Expansion of the current operation should lift output from 850 tonnes per year to 2,800 tonnes in the medium term.

I also like the business because work at Uis will also give it significant exposure to lithium and tantalum. AfriTin hopes drilling work at the site will lift the resource estimate from 71.54m tonnes of tin to 200m tonnes of tin, lithium, and tantalum. Lithium demand should rise strongly along with sales of battery-powered electric vehicles.

Riding the electric car boom

Surging tin prices have helped blast AfriTin Mining’s (LSE: ATM) share price through the roof. The penny stock recently closed at record peaks of 7.8p per share but has sunk from these highs due to choppy metal prices. I think this could represent an attractive buying opportunity.

As its name suggests, the business is involved in producing tin in Africa (and more specifically Namibia). This is a commodity that could be set to soar in value as demand for consumer electronics and electric vehicles (EVs) takes off. The metal that AfriTin produces is being used increasingly as a soldering material instead of lead.

But the commodities producer is about more than just tin. AfriTin has spoken previously about adding tantalum and lithium to its product suite and this month announced it had found spodumene near its flagship Uis asset. The lithium-bearing mineral could significantly boost AfriTin’s exposure to the booming EV market where it is used to make batteries.

AfriTin has plenty of potential, then, but its shares don’t exactly come cheap. The business trades on a forward price-to-earnings (P/E) ratio of 23.3 times. It’s the sort of premium rating that could prompt a sharp share price reversal if the company experiences trouble.

However, this is a risk I could be willing to take given the excellent long-term potential for its metals.

A safe-haven penny stock

The Covid-19 crisis and tragic events in Ukraine show that holding gold, gold-based financial instruments, or precious metal-producing stocks could be a good plan. History shows that bullion prices rise during social, economic, and political crises when riskier assets like shares sell off. So having a gold-based investment at all times can help protect one’s portfolio.

This is why I think holding Shanta Gold (LSE: SHG) shares could be a good idea for me today. Buying this particular gold miner gives me the chance to receive dividends along with the benefit of riding the gold price. This is something that owning bars, coins, or a metal-backed financial instrument like an exchange-traded fund (or ETF) doesn’t. Oh, and the yield at Shanta sits at a healthy 2.3% for this year.

Gold prices came within a whisker of reaching new highs last week as Russia intensified its operations in Ukraine. The conflict is ongoing and so fresh attempts could be around the corner in the coming days. Regardless, I think bullion will take out the current record above $2,070 per ounce as inflationary pressures accelerate. The Bank of England, for example, now says British consumer prices could rise more than 8% later this year.

Owning mining shares like Shanta Gold means that investors burden themselves with the extra risk of production problems that could decimate profits. But it’s my opinion that the potential long-term benefits of owning this particular Tanzania-focussed miner still make it a great buy for my portfolio right now.

Even the best penny stocks to buy can be prone to extreme share price volatility though. But as someone who invests for the long term, the prospect of some choppiness doesn’t put me off. Like any other UK share, I’m confident that with the right research I can find low-cost stocks that should rise in value over a longer time horizon.

Here are two such penny stocks I’m thinking of buying in September.

Tin star

AfriTin Mining (LSE: ATM) is a share that’s not without its degree of risk. The process of digging for raw materials is a costly and complex endeavour and problems can be common that can significantly hit the bottom line. What’s more, the company trades on a price-to-earnings (P/E) ratio of around 19 times. This sort of valuation could prompt a share price correction if confidence in the company starts to wane.

That said, this is a penny stock I’m paying very close attention to. AfriTin’s share price has risen 160% over the past 12 months, carried higher by an electrifying rise in tin prices. The soldering metal recently hit record highs of around $36,600 per tonne. And I think it could keep going as Covid-19-related supply issues drag on and demand from the consumer electronics sector rises strongly.

I also like AfriTin’s plans to add lithium and tantalum to its product suite. Lithium uptake looks set to soar thanks to its critical role in powering electric vehicles, a market set for explosive growth. And tantalum demand should rise as global smartphone production steadily rises.

Another thriving penny stock

Glenveagh Properties (LSE: GLV) is another penny stock I’m thinking of buying today. The Irish housing market is suffering from the same supply crunch as here in the UK, a dynamic I’ve sought to play by buying FTSE 100 stocks Barratt Developments and Taylor Wimpey.

Latest financials from Glenveagh have illustrated the great investment potential across the Irish Sea. All 1,150 properties it plans to build in 2021 have been sold, the builder said, and a further 300 that are scheduled for next year too. Unsurprisingly, Glenveagh is ramping up production to make the most of this environment and it expects to build 3,000 homes a year by 2024.

Home price growth continues to pick up steam and latest data showed the average property value jumped 6.9% year-on-year in June. A major shake-up in housebuilding policy is needed to soothe the supply and demand imbalance and stop prices from continuing to rocket. But signs of progress on this front are not yet forthcoming, meaning that profits at the likes of Glenveagh remain on course to continue booming for some time yet. A word of warning, though: this penny stock is still highly cyclical and so a severe economic downturn could hit demand for its product hard.

This sounds promising. But as an investor, I want to know if the price increase can be sustained. For this I took a look at its fundamentals, which are a mixed bag. First, the positives:

#1. Decent operational update

For the March–May 2021 period, AfriTin Mining produced 183 tonnes of tin concentrate, higher than the company’s 180 tonnes target. It also extracted more tin metal from the concentrate, at around 59%, than in the same quarter last year. 

It is also looking to implement a project that will enable it to extract a higher 67% tin from concentrate. Tin prices are at multi-year highs, which should strengthen the company’s financials in any case. But I think it can gain even more if this project pays off.

#2. Possible lithium production 

Earlier this year, it also talked of adding lithium to its products. Lithium is a component in electric vehicle (EV) batteries. As the popularity of EVs rises, lithium demand is also expected to rise. According to S&P Global research, lithium battery production capacity is expected to increase by 26% each year on average over the next five years.  

However, there are downsides to the AfriTin Mining share too. These are:

#1. Weak production and financials

Its latest production numbers may be higher than expected, but they are less than those in the same quarter last year, at 195 tonnes. Also, it is a loss-making company, and I am not sure when it will start making profits. As a rule, I like to buy shares of loss making companies only if they are growing fast or it is a one-off occurence, like during the pandemic. Neither is the case here.

For this reason, I would put it in the category of a speculative investment. It is not as speculative as say a bitcoin miner but it is not as safe as an established FTSE 100 or FTSE 250 miner either. 

#2. Other miners outperform

Moreover, some of the more established miners are better buys right now. For instance, the FTSE 250 iron ore miner Ferrexpo has seen a far bigger annual price increase of 144%. Even FTSE 100 multi-metal miner Anglo American has seen a bigger increase of 71%. Also, both of them pay dividends. 

My takeaway for the AfriTin Mining share price

On a net basis, I think that AfriTin has some merit. With tin prices on fire, potential for increased tin production and even lithium production, it is possible that its share price can continue to rise. 

However, I also have to bear in mind its recent performance and its weak financials. I think there are more robust stocks to buy today that can perform equally well if not better.